Believe me, even a mature software for a new customer is something new, because they usually want additional features, e.g. (in this example) cross-references, that weren't there before. Or an integrated ordering system or a different database structure behind it due to a different hierarchical assembly organization and so on. Let alone DRM barriers to protect unauthorized copying and printing.
The other thing is the population with data as you mentioned. There will probably be a lot of open ends pointing to another subassembly and things like that. I'd be surprised if they actually got that done since the Grenadier is still a moving target.
But I agree that a beta-testing group made of "non-biased" users is a good idea.