Yes, that rings a bell. 
I have no problem if SWI-Prolog does not use semantic versioning.
Perhaps the SWI-Prolog Versions page should note that while the SWI-Prolog version pattern is the same or similar to semantic versioning it is not actually semantic versioning, then that would end any possible connection and there would be an authoritative reference for future questions on such. 
Much of what you noted in the reply is very useful and nice to see elaborated (will repost parts as a separate nice to know topic).