To add to the dilemma, they also used AX on some of the SG MofW. And still, there is nothing concrete to say that cabooses, for instance, are not O (Oh) 500 in stead of 0 (zero) 500! Nor to confirm that the other series isn't 0 (zero) M for the rotary!
And early computers were aware of zero and the letter O. The problem may have occured when zero preceeded the significant digits in a number. And there is nothing to say the data entering entity wasn't entering a zero when it should have been the letter O!
Just more food for thought.
Robert