Lifejacket Location
Yes, of course all the aircraft come from Boeing, but over a period of years! If Boeing decide to introduce a mod to relocate the LSJs then the new aircraft will have them up top and old ones will have them under the seat and the difference cannot be sorted out overnight on a fleet of 100+ aircraft. Listen to the briefing, check under the seat and relax once you have worked in which one of two possible locations the thing is! How easy is that?