ABA question

[DET63]

When trains had B units, it seems like they were often run between two A units, with the A units run back-to-back and the B unit in between. Was the B unit permanently "married," at least as far as its numbering was concerned, to one or both of the A units? Let's say the lead unit was 1001. Would the B unit be 1001B (with the A unit then being 1001A) or 1002 (and the third unit being 1003)? Or did different railroads have different practices (e.g., using a completely unrelated numbering sequence for the B units)?

 

[JAChooChoo]

................ Or did different railroads have different practices (e.g., using a completely unrelated numbering sequence for the B units)?

Yes. For more detail visit the websites for the various historical societies related to each railroad.