7470,
As you interpret it, the 1472 is kind of complete re-build. This rebuild is mostly boiler oriented, but can pass on to other aspects of the locomotive as well. Usually when a 1472 is required, the locomotive has other issues (like running gear, cellars, boxes, bearings...etc work that needs done). The most economical sense is to do all of this work at once due to the fact that if you are tearing the engine apart (pulling off the jacket/insulation etc) it makes everything a whole lot easier to do for the rest of the rebuild.
In terms of the engine you are going to talk about, I am going to make an educated guess based on your screen name. I have a few BIG beefs with their argument as you have stated, and I quote "one steam locomotive in particular that is used only periodically despite much popular demand. They claim that the limited use complies with the FRA's 1472 day or 15 year operating days section as if to say that by limiting operating days they use the locomotive, they will prolong the complete overhaul."
1. The part 230 you I sent you (and you have been reading) allows for what is called "out of service credit". This out of service credit can be put towards the time the locomotive goes between it's 1472 day inspection. You are right in assuming that it will prolong the 1472, but when it comes right down to it, if they want to run steam they will run steam. The quote above sounds like it comes from people who don't have a good steam program, and either can't or don't want to hire "real" steam guys to work on the engine. If that is not the case then they are CHEAP and headed for a Gettysburg of their own. Saving for the 1472 and having people who are certified to do it (like a lot of steam programs do) can alleviate a lot of these issues long before they become a problem.
2. Remember that the steam world (people that can really run/work on them) are a dying craft. To get people hired full time to work on it you have to be willing to pay for them, and the 7470's owners are C-H-E-A-P, cheap! the deferred maintanence program that they practice may be very good "smoke and mirros" now, but when it comes time to put the engine out, they have to scramble last minute to get the FRA inspectors there. Beware of programs like that which don't really show REAL progress on the locomotive. Reading 230 and the safety rules, you should see more of what I mean. You have all ready seen some, now learn some more. You young guys are the future of our hobby, passion, and the engines we have worked so hard to save.
Character is doing the right thing when nobody's looking. There are too many people who think that the only thing that's right is to get by, and the only thing that's wrong is to get caught. JC Watts
Knowledge is knowing a tomato is a fruit. Wisdom is knowing not to include tomato in a fruit salid.