> the Rhineland "Session", which begins in November, is somewhat awkwardly interrupted by Christmas and ends with Carnival

Wait, tell me more about this? I've never heard of it but this sounds much more similar to what is practiced by eastern christians. Where there is also a 40 day fast before christmas, then the twelve day feast ending with epiphany/theophany. And in those branches lent itself is preceded by a 3-week period of increasingly strict fast. So in some years depending on when easter lands you can start fasting again very shortly after christmas ends but is still understood as a completely separate thing.

I don't know anything about the rhineland one but I could see how this could eventually mutate into one super long fast with a break for christmas, but also maybe isn't seen that way by the people doing it.

Ah, no, sorry. This would be more like the opposite of that: An extension of carnival itself into a period of several months.

According to that timeline, carnival "really" begins on November 11 (11/11) with a one-day celebration, then goes on in a low intensity sort of way all throughout winter, to end with the celebrations of the traditional festival.

It seems to have been a 19th century invention and in effect decouples the celebration from its religious role.

https://de.wikipedia.org/wiki/Karnevalssession