I came across this problem that my A3000 had channels 0,3 right and channels 1,2 left and my A1200 was the opposite.
Note that in fact the RKRM Hardware Reference Manuals themselves contradict each other!
Hardware Reference Manual (1st Edition 1986): Page 136: Channels 0,3 left and Channels 1,2 right.
Hardware Reference Manual (3rd Edition 1991): Page 137: Channels 1,2 left and Channels 0,3 right.
Looks like whomever wrote the later manual (be it starting from 2nd or 3rd edition) swapped them around for some reason given that the details are in the same respective sections of the manuals. I do not have the 2nd edition to check that.