Mexican 92.5% Silver 1 oz Bullion Balance Scale / Libra / Balanza (1978-1980)

StevenDS · January 4

I'm sure the Libertad fans on the forum know the bullion predecessor of the Libertad.
Not sure what's it called exactly, but I have mostly seen it referred to as either 'Onza', 'Libra' or 'Balanza' (Balance Scale).
As you can see on the pictures, one side has a balance scale and the other a press.
It's Sterling silver (92.5% silver), but contains 1 oz of silver.

They have only been minted for 3 years. Excluding the 1949 version which is slightly different and was minted from between 1949 and 1978, but all showing the 1949 date.

Unlike the Libertad series I can't seem to find any mintage details.
Does anyone know a good resource to check?
The early Libertad's had a mintage of approx 1M each year, so I'm expecting more or less the same, but would be good to get some confirmation.
Would be also interesting to know whether there are significant mintage differences within those 3 years of mintage.
First year 1978 seems to be most difficult to find.