John,
I agree that I've never heard the term "rebuilt" used by anyone associated with Railroad, unless it was used to describe work done.
The word "overhaul" was always used in my experience to mean major shop work, that took an engine out of service for a long time.
To get it right, it should be assumed that #481 was really the last engine overhauled at Alamosa, because in addition to major mechanical work, the boiler was completely refitted with new flues and stays.
#497 received some mechanical work, and so did #473 after #481 was completed, but I doubt either would really be considered an overhaul.
#488 is being overhauled now. That's an overhaul as I have always understood the term.
Thanks for addressing the fine tuning these terms.