how to identify that manpage is only for certain platforms?

Various manpages refer to other manpages (.Xr) that don't
exist in default 
manpath.

Using arch directory name, like:
.Xr &mac68k/ae 4
seems okay if that is the only ae(4) manual page.

But what about few manpages that refer to asc(4)? But asc.4
is for a few 
ports like: acorn32, alpha, pmax, and vax.

How should those be handled when refering to them? List it
four times 
(with "port/")? Have some comment about the ports?
Or just ignore it -- 
causing frustration for those trying to get more details?

  Jeremy C. Reed