Hi Scott,

Guide has elements built into it for comets before the CDs were
made. So you should have no trouble in finding those ancient
20th century comets.

All you'll get from MPC are the more recent objects, and it's
not an exhaustive list, as you've found. Ideally, I'd prefer
to make use of the JPL list of comets:

http://ssd.jpl.nasa.gov/sb_elem.html

...which contains everything going back to about 1996 (except
SOHO comets). The only problem with it is that it lacks magnitude
parameters. JPL _has_ those parameters -- in fact, it even has
the separate parameters for nuclear and total magnitudes. But
you only see them when you query individual comets; you can't
just grab their entire list of comets with mag data. (I've
asked for this to be changed.)

The omission of SOHO comets is no biggie, since the data
exists at

http://www.projectpluto.com/soho.zip

(though again, without any magnitude data).

-- Bill