Hi! If you mean the serial number, this is just the date (YYMMDD I believe) the game file was compiled. If it's version number, the latest should be 4 (just a printing error corrected from 3 though). The game won't be updated further (and I don't keep track of interpreter enhancements) so that's the final release number!
I hope that helps :) And great choices on these physical releases!!
When you view the list of downloads, versions go up to 9 (Gameboy Advance) for some, and much lower for others (2 for PSP). I wasn't sure if a version 9 might have some corrections not in a version 2.
I ended up going with the Commodore Plus 4 version to play both because it was a version 9, I wanted to use a kb, and the emulator has a nice curved CRT filter. I also wanted to learn to load stuff on a system I'd never used before. That's been working great so far.
