.
Man...

https://en.wikipedia.org/wiki/Earth-616

https://en.wikipedia.org/wiki/Marvel_Universe

... as if the Marvel continuity were not already complicated enough.

It's gratifying how viscerally both editors Tom Brevoort and Joe Quesada thoroughly reject the "Earth 616" term.
As apparently do many others in the Marvel offices they refer to but don't name, as staff who agree with them and don't use the term.



I actually read these Dave Thorpe, Alan Moore and Alan Davis stories about 25 years ago, reprinted in the U.S. in a title called X-MEN ARCHIVES 1-7, and at the time didn't realize they had any significance at all, that apparently spawned the idea for this "Earth 616" thing.
The Thorpe, Moore and Davis stories were apparently given a greater significance retroactively by other writers and artists in later storylines.

all 7 issues at :
https://readcomiconline.li/Comic/X-Men-Archives-Featuring-Captain-Britain