I do not see any example of it being for example 2.x.y.z, 3.x, or something other than 1.x… Is it automatically assigned? Can I change it? Are there cases when “1.” finally goes up?
Yes. In the current bk source, a revision always starts with 1. And the revision numbers are not stable, after a merge the revisions can get renumbered. (see sccs_renumber() I think)
The numbering scheme has completely deterministic so two repositories with the same file will have the same revisions.
We did have some schemes that took advantage of incrementing the first number, but they are not in the current code.