If a later port added it back in then that is one thing, other regions can have stuff cut for whatever reason, if the source came with one of the gigaleaks then that, if one of the original devs or testers spoke/is willing to speak of things and remembers it, if the game's code has a bunch of leftover data where it logically should be if the table(s) of stats and whatnot continued , if the game's code has some obvious jump or blanked out branch to a piece of code that never gets taken then that could yield something.
For older games then assembly development does mean you stand a better chance of something still being tucked into the code compared to newer stuff that would have seen it lost in a recompile.
As the earlier stuff there is unlikely to yield much you are left with analysis. In that case find the tables of various move stats, or the logic of what move gets picked (I would probably work backwards from a player being hit and it taking health away -- work back from there far enough and it will be deciding upon the move and then you can analyse the branches and locations around where they might land).
Sometimes there is inference as well; if for some reason wherever they are found has a lot of poison antidotes but nothing really poisons you then there is that. Beyond that you are left with pure luck type things where some random data used to pad something just so happened to be an early copy of something, which I am not expecting here.