mandoc has no version parameter. If you want to know which mandoc version is installed, you have to read the source in src/contrib/mandoc/Makefile It would be great if mandoc has a version parameter (e.g. -v) GNU groff works fine: $ groff --version GNU groff version 1.23.0
upstream will never accept a version parameter as far as I can tell, at least this is the case for most things that comes out of openbsd. (Maybe you can ask Ingo he may have an opinion)