Actually there isn't much difference in the MKIII and the MKIV. The MK4 can have more memory and can have more memory added on it's SCSI controller. But seeing you have the full MKIII (50Mhz instead of 40MHZ EC) you won't notice much speed difference.
Also, I have not yet found a 128MB SIMM which fit's the MKIV without having to use rubberbands, far from ideal.
If you want the SCSI controller then yes, a IV is better available then the MKIII scsi...
But seeing that the bag was labeled MK4 could mean it was a genuine mistake. Altough the fact the rev label is scratched out worries me a little....
