In the early days of PC C compilers Microsoft and Watcom were far from the top dogs. The market leaders were now-forgotten compilers like Mark Williams C, Lattice, and Manx.

Depends on what you mean by "early days". If you're talking pre-1987, you might be right. 1987 and beyond, Microsoft and Watcom were big ones (and yes, Lattice was a big one as well). Microsoft was becoming a corporate standard for C compilers by 1987 - the source-level debugger (CodeView) was a big reason.

I know the history from 1987 and beyond pretty well - before 1987 I'm very hazy.

Wasn't Mark Williams on other platforms? Again, my memory before 1987 is hazy.