I can tell you the difference between Donkey Kong Country 1.0 and 1.1.
You can turn Winky and Expresso (The frog and ostrich) into Rambi (The rhino). I figured this out myself and it didn't work on cartridges my friends got that Christmas (I got a November '94 copy)
Honestly, you never know all the differences because it's a secret that different versions even exist. I told the ROM database creators about the existance of a second version of Killer Instinct because the one included with the SNES Killer Instinct bundle did not function with the XBAND (SNES multiplayer modem). They didn't believe me until years later, when some guy "happened" accross one at a flea market, dumped it and was surprised to find out that it was different. It made Cherryrom's "ROM of the Fortnight."
BTW, the [!] means that it is a confirmed good dump and not a corrupted ROM. It's in the GoodSNES readme file (The database which created the naming nomenclature/schema). The creators of the database basically dumped their own copy and did a byte-for-byte comparison, or discovered the new version with their own dump. It means that they did not stumble accross a modified or corrupted ROM on the Internet, though all known modified and corrupted ROMs are also added to the database (The GoodSET includes all known beta versions and ROMs with unknown origins also).