That’s a good point that openSUSE containers on dockerhub automatically default to latest current stable… I don’t think that even official 15.0 images are available. A case can be made that 42.3 is no longer supported, so should not be available anymore.
In any case, it’s pretty easy for just about anyone to make a private (not officially openSUSE) image of anything, so a 42.3 container can be created if there is reason and demand for such a thing.