I can speak only for one railroad. On the T&P the engine number followed the boiler. According to an official I talked to, If the engine number did not have that particular boiler that led to all kinds of records having to be made for ICC boiler people and was really a headache. But, understand there were 70 engines (2-10-4). When getting major shopping if the shop had a running gear ready from say 630 and a boiler that been on 655 the two would be mated and the engine number would be 655. They would not hold up having a serviceable engine to keep the same boiler and running gear together. Some boilers required more work than others.
The tender number would be changed from 630 to 655.
I don't know about the Rio Grande. But , I do know that additional records of the number change would have to be kept for the ICC boiler people.
Edited 1 time(s). Last edit at 08/20/2018 07:39AM by Tomstp.