Athearn Chessie Geep query

[WHOPPIT]

Hi, ive just picked up a chessie geep 38 by athearn, its numbered 3577 and is marked 'W&M' instead of 'WM'! I cant find any record of this being made, was it a mistake in the factory?
thanks
paul

CSX - Chessie Still Xists! graemlins/notworthy.gif

[CP&E 3207]

The prototype of 3577 is a GP35. I found a picture of it and it just says "WM" so it must be a factory "oops."