Ah that would make a lot of sense. Your answer that is, not the decision by peugeot to change the names. Also strange is the change of fork material; i've seen earlier ventouxs with a 501 fork. My bike, we'll call it a Nice now haha, is only 3 tubes 501. It does have a strange reynolds sticker that i've only seen a few other examples of. The Bottom part that typically says Ti Reynolds Limited says something like Ti Reynolds 531 Limited. Might not be in that exact order, but for some odd reason has a 531 thrown in there. Have yet to understand what that's about.

I'd like to see more pictures of the OP's bike/part lists. Mine has had some changes made, i.e. a Miche Competition hub.