calibre versions as we think of them are major.minor, but really they were released as 0.something major versions until 1.0, then they got numbered major.minor.patch -- with nary a patchrelease in sight.
Lots of current releases are bugfixes, the release numbers indicate weekly snapshots (advancing a major number is when you can say "important stuff just happened"). Kovid did say he was at some point going to use patchreleases for occasions when a rerelease for critical bugs needs to be done.
Yeah -- the format has been there for a while.
See:
https://github.com/kovidgoyal/calibre/tags for a handy listing.