Somewhat on topic: I think it would be nice if as a community we could come up with a list of all code variants. I imagine some codes are a lot rarer than others and most of us are blissfully unaware.
On a similar note, the first EX Emerald Pichu code in the spreadsheet is “BSW-3XN-B31”, however in 2 weeks since leaving this post I’ve not seen a single example which has this code. I’m wondering how some of these codes were verified when that spreadsheet was created; I’m guessing it may have been an assumption based on the Luvdisc and Spoink cards which also have B31 variants alongside JCR and CUU (like the Pichu) - these, however, seem very easy to find.
Update: Found one!