Sega Master System / Mark III / Game Gear
Differences between versions: v0 (CRC:868419b5 ) is most commonly found in the cartridge release, v1 (CRC:5a904122) in the card release. However some card releases contains the v0 ROM.
The two dumps differ only in the range $2f16 - $2f7b. In v0 this range is filled with genuine code. In v1 there is code from $2f16 - $2f49, followed by a jump to $2f7c. The remainder of the range ($2f4d - $2f7b) is filled with NOPs.
It seems that between the two versions a change was made to the code starting at $2f16. The new code turned out to be shorter than the old, so a jump and several NOPs were added to preserve the location of the remainder of the ROM.