It is my understanding that most programmers would expect a version number of Major.Minor.Patch to be semantic versioning. Since a change in a Major number indicates a breaking change then I would expect something to have broken.
Over the last few years of seeing the SWI-Prolog releases and the corresponding numbering the only things I know for certain are
- The numbers do increase and are sequential
- When the second number (Minor) is even it is a stable release
- That version numbers created from a Git Pull have the commit hash appended.
- There is another variation of the version that I see so rarely I can’t remember off the top of my head.
- The stable versions at times do increment the Patch value if a backward patch is made.
- There is a documentation page on version numbers: SWI-Prolog Versions
Personally I like seeing software with low Major numbers and large Minor numbers even with Minor numbers in the hundreds if the really are following semantic versioning.
EDIT
After reading reply by Jan W.
Example of DIRTY version. (ref)
SWI-Prolog version 8.5.7-26-g4a0a2091e-DIRTY