It seems that everyone but me remembered that tm_year is still based
   on a 1900 offset.  I guess we should note this in the
   ctime(3)/mktime(3) man page, which is what I looked at to remind
   myself of the calling convention.

It's in there, albeit tersely:

                   int tm_year;     /* year - 1900 */

Can you suggest some additional text which would have made it obvious?

					- Bill