Robert:
The information about the X and 0 problem comes from D&RGW documentation in my hot little hands.
Cabooses and all MOW equipment except for the OA-OZ series use the digit 0 instead of the letter 0 and this again is from D&RGW documentation. I am writing a two volume history of D&RGW snow fighting equipment and my information is all directly from D&RGW files.
The X replaced the 0 due to computer limitations. They added the A to indicate a car that could be placed anywhere in a train (had couplers on both ends). The computer was not reading the 0 and some non MOW freight equipment with the same number (minus the 0) was being mistaken by the system. This also was shared with me by someone who worked in the D&RGW Burnham Car Shop for many years.
Jerry Day