Termcap, IC, and IM

[Jym Dyer]

Gotta question for all you termcap gurus out there.

I've got several termcap documents.  One is Richard Stallman's excellent
 Termcap manual.  It tells me that if just inserting a character in insert
  mode (IM) is sufficient, there's no need to define insert character (IC).
   A DEC manual says that if you do define IC, IM should be defined in the
    termcap file as ":im=:".

Is there ever a case where an insert mode won't let you insert without
 using an insert character escape sequence?  If so, what kind of insert
  mode is it?

I'll tell you why I needs to know.  I've got code that runs on Unix that
 I'm porting to VMS.  I've written a version of setterm() for VMS that gets
  information from VMS' termtable file and puts it into Curses variables
   (IC, IM, etc.).  Unfortunately, the termtable entries for DEC terminals
    give values for both IC and IM.

Things work if I just ignore one or the other, but I'm not sure it would
 work on all terminals.  Does anyone know (1) what logic I should be using
  if I have both IC and IM, or (2) what terminals need both to insert?
   <_Jym_>