Making tons of backups is always a good idea...
Anyway, I don't know how corruped your main rom got but perhaps you could transfer some data from it to the older one that you're working on right now.
To do so, I'd suggest you to use Notepad (it's not that simple as notepad shows the bytes as some odd marks but you should be able to find the right spot if you make the rom even more glitched up by for example replacing all data in front of the offset you want to copy & paste to your older rom with one single byte (like 00)).
Not sure if I made sense but here is an example.
Let's say you want to transfer the data between offsets 0x19000 & 0x19A00 to your older rom.
First open the corrupted rom with hex editor and go to some offset in front of 19000 and re-write all the bytes with 00's and do the same at 19A01 -->.
Then, you should be able to find the right spot in Notepad where you just copy all the odd marks between the ones shown as 00 and paste them to the same spot in your older rom.