I guess it's a competence thing. I've worked on UK MoD and US DoD contracts (and many others) for most of my adult life. Routine contract amendments happen most months on all of these due to oversights, enhancements or simply changes in the world around us. We handle these as normal business - it's a routine part of the day job for the commercial and PM staff. But I have to assume from what you say that Boeing doesn't employ competent staff in these roles. It would explain a lot.
PDR