As this is a suggestion for a formal convention, I suggest the following corrections:
The way the metal of the coin is specified needs to be more consistent:
1btc Coin, S2, 2013
1btc Silver Coin, S3, 2013
...
0.1btc Brass Coin, S2, 2013
0.1btc Silver Coin, S2, 2013
The brass material is "Coin" for CASASCIUS and "Brass coin" for LEALANA.
My opinion is to either include the material or not, but it must be consistent.
The placement special attributes (nick names) also needs to be more consistent:
1btc ‘First Bits Error’ Coin, S1, 2011
5btc Coin, S2, 2012 ‘Bitnickel’
In the 1 BTC is the special attribute the 2nd paramenter, while for the 5 BTC is it the last.
My personal opinion is that all "nicknames" should go last.
The face value should be either "1 BTC" with capital letters and a space, or "
BTC1".
My opinion is to use "1 BTC".