Nobody said it didn't evolve, and you're the first one to use the word "proper" which has a much different connotation than "traditional." Think of it as a snapshot in an event-sourced system. You can take a bunch of snapshots over time, but #53 is going to be the same every time. A "traditional" lasagna has a bechamel sauce. You can make it without, and it can be as good or better. It just won't be traditional, which is totally fine.
I'm not Italian, but my impression from traveling in Italy is that every town\village\grandma has their own version of nearly every Italian dish and they all consider theirs to be the traditional version. I think I got told three or four times that I was in the village where focaccia was invented - different villages, that is. And they were all quite different focaccias so I guess they were all right.
Side note: bechamel lasagne is usually called lasagne al forno and I think it comes from Bologna. In many other parts of Italy they don't use bechamel in their traditional lasagnes, and they often do use ricotta and mozzarella.
