thanks @LawrenceChardand @Foster88 for sharing your thoughts on that;
it is true what you both say about auctions; consider that a lot of collectors (like me, i m italian living in italy) have very few chances to meet with UK coin dealers, to go to fairs, to actually see and assess personally coins in hand... and especially with Covid, travelling has become much more difficult, and sometimes unsafe..
online auctions are going to be more and more relevant in the future in my opinion, and slabs are perfectly matching with this trend. Its a guarantee (even if i got the impression that most people buy the slab with the magic number, rather than the coin within..)
going back to those 3 rare coins, and if i were to make a catalogue, i would re allign prices to what the market is saying/asking today. There has been a run for sovereigns in the last 2-3 years and victorian shields in high grade are getting scarcer and scarcer.