Okay, it seems to be pretty clearly that the TIFF library is pickier.
(I found an old TIFF file that I have previously been able to display,
but which I can't do anything with, now.)

So, what graphics software might I use to convert these files to
something that the GIMP could use?  netpbm's tifftopnm seems to have
the same problem as the other software that I've tried.  I also have
just tried fbm, and it complains about "unknown magic number 111".

-- 
  "I probably don't know what I'm talking about."  http://www.olib.org/~rkr/