Hotdog

Photo of coin is the most important thing. Who is to know how those coins were stored over so many years. They could have been in a damp cellar.  At the end of the day, you will be selling a proof coin, not a promise that there might be a nice proof coin in the box.

wow - it takes some serious restraint not to open up these coins over the last 32 years 
Im usually like this guy the second after the postman left! 

 
I think buyers would need to see the coin before purchase - they could be copper spotted in there.  Maybe throw in an unboxing video.  

The coins, of course. Better still, place them in some NGC plastic coffins and raise your price by 50%.

Closest I have is an 1887 Melbourne second legend DISH.M8. Pearls are similar, dots in neck , tail and dragon all look similar too. Weight is 7.99g diameter varied from 22.119 to 22.037 (don't usually use the micrometer but my son has 'borrowed' my calipers!).

An interesting read is "Counterfeiter" The Story of a British Master Forger. Its the story of Charles Black (born Lewisham 1928) co-written by Michael Horsnell in 1989. He mentions that one of his associates made a fantastic living from sovereigns made in Switzerland from Lebanese dies (which reputedly contained a high amount of gold) and sold them at a high premium in London to well known concerns in the 60s. 

The "other site" you mentioned probably got their information from here:
https://24carat.co.uk/frame.php?url=collectingcoins.php
"What premiums would have been paid in past decades?"
Although you did not say which decades, or how many:
About the same as now, apart from 2008/9 when almost everybody, except for one Blackpool dealer, stuck their premiums up to take advantage!
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A well known Blackpool dealer usually pays spot for sovereigns, and only occasionally less if they / we get far too many, or if there is a big gold price spike. Even then, it is 99% not 98% or 97% which some of the scrap dealers pay.
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I started stacking 12 years ago and my sovereigns and half sovereigns were mostly purchased from HGM and BbP ( but some on eBay ) with premiums over spot between 2 and 3 % - MAXIMUM.
Bullion sovereigns weren't categorised by Monarch so these dealers just called a sovereign a sovereign and didn't care about dates and stuff selling on a FIFO basis generally the same day.
Some days these companies only had a few coins to sell and often none at all.
Now with many more people collecting and buying coins these bullion dealers have morphed into coin shops and many premiums are ridiculously high, but that's maybe what the market will bear, although I see this more "opportunist" if someone is so desperate to acquire a specific date.
Selling back to them, whether a Victorian shield reverse, or an FDC certificated proof, only gets you 97 - 98% ( 100% maybe but I've never had that offer ) of spot most of the time.

Still think this is an interesting coin.
if anyone  has a similar coin it would be great to see a high def image.  The ones I have seen are way less detailed.
 

The photos attached show a 1887 Jubilee sovereign, Sydney mint. I believe its a short tail, hooked J, first legend, DISH S1, Spink 3868A, Marsh 138 (though happy to be corrected).  
Weight is 7.947 grams. What's bothering me is the diameter which comes in at an average of 22.31mm after multiple measurements (avoiding the obvious dings on the edge. I did several SG tests and they averaged 18.39. Thickness appears normal, and the colour is similar to other Australian sovs that I have. 
It has a good ring/ping sound to it, though does not meet good on computer apps (precious coin tester, bullion test) for measurement of frequencies, though I wondered if this could be down to the diameter being over size? Marks on the coin would indicated that it was mounted at some time in a ring or similar. Anybody out there with the same year/mint/coin/measurement?

Quite a few people have recently reported concerns about the actual diameter of gold sovereigns, or half sovereigns.
It is not something that I have paid particularly close attention to in the past.  This is probably because when looking for fakes, there are much more important things to watch out for, and I have always been aware that there is some tolerance.
I commented recently that I should check what the stated tolerances are, but meanwhile I would not worry much about yours.
Interestingly, I just noticed that Wikipedia incorrectly states the diameter as 20.0 mm:
Sovereign (British coin) Diameter 22.0 mm Thickness 1.52 mm Edge Milled (some not intended for circulation have plain edge) Composition .917 gold, .083 copper or other metals  
The Royal Mint do state it correctly:
The Sovereign 2020 Gold Bullion Coin Specification Value Diameter 22.05mm and so do Chards:
Sovereign Technical Specifications
Diameter (Millimeters)  22.05 Weight (Grams) 7.988 Alloy (Carats) 22 Fineness (millesimal) 916.6 Actual Gold Content (Grams) 7.322 Actual Gold Content (Troy Ounces) 0.2354 Although Wikipedia is often a good source of information, I often find errors there when it comes to coins.
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Thanks for your comments. Forgot to mention its a single sov.
The "odd dot just adrift from the dragons head" is part of the dragons "Frill" and maybe seen on the 1989 and 1890 Sydney Jubilee sovs. https://goldsovereignexpert.com/coins/151/1890-Gold-Sovereign-Victoria-Jubilee-Head-St-George-Sydney-Mint/
Die alignment looks good. The edge does look uneven in the photos I attached, though I think that's more down to the light coming in from my window to one side of the coin.
I'd still like to hear from anybody that may have one with the same oversize diameter. Will knock up a couple more photos tomorrow, with different lighting.

The photos attached show a 1887 Jubilee sovereign, Sydney mint. I believe its a short tail, hooked J, first legend, DISH S1, Spink 3868A, Marsh 138 (though happy to be corrected).  
Weight is 7.947 grams. What's bothering me is the diameter which comes in at an average of 22.31mm after multiple measurements (avoiding the obvious dings on the edge. I did several SG tests and they averaged 18.39. Thickness appears normal, and the colour is similar to other Australian sovs that I have. 
It has a good ring/ping sound to it, though does not meet good on computer apps (precious coin tester, bullion test) for measurement of frequencies, though I wondered if this could be down to the diameter being over size? Marks on the coin would indicated that it was mounted at some time in a ring or similar. Anybody out there with the same year/mint/coin/measurement?

Your question shows a basic misunderstanding of the coin production process, which as you will be aware is in multiple stages and sub-stages.
Broadly, you need to think about "Die Production", which is a whole complicated process in its own right, and "Striking", which is very simple.
First "Die Production". I do not know the precise process, or every detail of it, but in any case die production has evolved over millennia, and parts of the process would have changed during the reign of Victoria, so someone with intimate knowledge of modern day die production would probably not know the fine details of the process used at any given period in the past. Similarly Victorian die-sinkers would probably understand modern processes if they could see them, but would undoubtedly be impressed, and possibly astounded, at some of the technological changes. Die production has always been a relatively labour intensive and expensive part of the overall coin production process. If you imagine the cost of a pair of dies as being around £1000 in terms of today's money, you will not be far out.
Each die would be made from an annealed piece of steeel, The main "device" (Victoria's portrait) would be stamped incuse into the die using a puncheon, which would have been of hardened steel, but with the design in relief. The lettering, date, etc, would then be hand punched into the die using individual letter punches, obviously prone to error due to lack of concentration. If the die-sinker noticed his error in time, he could attempt to correct it by over-punching it with the correct letter. As we all know, this process in usually not perfect, and can be detected, but only be fairly careful examination. The alternative would be to scrap the die, and start again. This would be relatively expensive. Once the whole design is present on the die, it then needs to be hardened, after which no further changes can easily be made.
The actual striking of coins, by bashing them between two dies, is a relatively simple, quick, cheap, highly mechanised (for most of the last 4 centuries) process. The cost of this part of the whole process is in the order of a fraction of a penny per coin.
Coins with an "F" over an inverted "A" were all made from dies, or most likely a single die with the "F" over an inverted "A".
There were probably none of the specific coins under discussion ever made with just an inverted "A". If any were produced, it is highly likely that they would have been undetected before leaving the mint and entering circulation, and some would have been spotted by now. I am aware that inverted "A"s do exist on quite a few dates, and I have not checked whether any exist in the place of an "F" on the date under discussion. 
What we can safely assume to be true is that no such error coins ever underwent a process of attempted correction by restriking them with a correct die. If this was to happen, it would be quicker, simpler, and more effective to melt them down, and replace them with new coins struck from the correct dies.
You ask "...how would the original faulty coins be aligned prior to re-stamping?" As you have imagined, it would be such a fiddly, time consuming, process that it would not be attempted, or even considered. It would also be ineffective, in that many of the "corrected" coins would show clear evidence of double striking.
"Are they manually corrected with and individual single letter punch, or some other process?". No, absolutely not. Even if someone attempted this, try to imagine how you would end up with a raised letter. Punching would only produce an incuse letter. Other methods do exist, but would be even more time-consuming. A highly skilled engraver could push some of the metal around to form a different letter, but it would be detectable, or a new letter could be transplanted into place using brazing or soldering, after first grinding or scraping away the incorrect letter. These processes are occasionally used by fraudsters to change a common date such as an 1962 (British) penny into a rare 1969 penny. I have seen an example, and written about it elsewhere.
The Wikipedia page partially explains matters, but assumes some knowledge of the production process.
 

Chards have posted this before on their web site: -
https://www.chards.co.uk/blog/analysis-of-alloy-content-of-gold-sovereigns/180

Reading "The Royal Mint" its working, conduct, and operations, fully and practically explained by George Fredrick Ansell, he comments that "The law enacts that 20lbs. troy of standard or crown gold shall be made into 934.50 sovereigns." It follows that the weight of a single sovereign is 123.2744783306581059 troy grains, i.e. 7.9880518266452649 grams; though reading further it becomes more complex with regards to the permitted tolerance. 
Reprints of Ansell's book are available online. 

Another reference: -
Lisle, George (1906). "British Currency: Gold". Accounting in Theory and Practice . William Green & Sons. p. 277.
 

Reading "The Royal Mint" its working, conduct, and operations, fully and practically explained by George Fredrick Ansell, he comments that "The law enacts that 20lbs. troy of standard or crown gold shall be made into 934.50 sovereigns." It follows that the weight of a single sovereign is 123.2744783306581059 troy grains, i.e. 7.9880518266452649 grams; though reading further it becomes more complex with regards to the permitted tolerance. 
Reprints of Ansell's book are available online.