TKaos is probably right here, sorry. It actually depends on the images and can be really hard to figure.
Explaining with an example:
Case 1:
Given a single, original disk. Imagine it was not write protected (or in case of dumps, the emulator altered the rom). You and me both have the exact same disk (or image). If we dump it *now*, we get both the same hashes as the disks are equal. However we both use them and they get modified - say, overwriting the highscore. Our once exactly equal disks were now modified, different from an untouched one. Dumping both would result in different files/hashes, for "Name (19xx)(publisher)[m highscore]", so one of them should have "[m2]", signaling a different modification.
Case 2:
This time we have 2 disks, they are the same game but with a slight difference, yours was released with harder enemies. Dumping both unmodified sets will now result in 2 different dumps "Name (19xx)(publisher)" and probably "Name (19xx)(publisher)[a harder]". This time, they were different from the start, even if they suffer similar modifications, say they were, again, played and scores overwritten. In my logic, they would now be "Name (19xx)(publisher)[m highscore]" and "Name (19xx)(publisher)[m highscore][a harder]", because, each of them was the first modified version of their scores. Got it?
The nice part about all this is it is ALL theoretical, in a perfect world it should work like that. The problem is that you're starting with the dumps already and many times (almost always?) you can't figure out what happened with such details.