Oh yeah, if you had registered for $12, you could play against a human opponent. Never was worth it for me though, especially as that'd have been an international payment and that was difficult for a kid in the 90's. I was just glad that the shareware versions were already pretty dang good.
I'm now just half wondering why they didn't release the full versions of their games for free a few years ago, when they suddenly stopped selling their games. Though apparently one can find unlock codes somewhere online to register those shareware games. I've not bothered with it so far but there was a whole Reddit thread about it.
Soleau really should refine those games for modern machines and release on Steam. ;)