Between the show's premiere in 1982 and the end of July 1986, the following weeks had fewer than five days:

11/22/82: Vicki Lawrence, Richard Kline - 2 missed days due to Thanksgiving

11/21/83: Didi Conn, Richard Gilliland - at least one missed day due to Thanksgiving

1/2/84: Rita Moreno, Richard Dean Anderson - 1 missed day due to New Year's Eve

11/19/84: Florence Henderson, Robert Mandan - 2 missed days due to Thanksgiving

12/31/84: Shelley Smith, Richard Kline - 1 missed day due to New Year's Eve

11/25/85: Abby Dalton, Ken Kercheval - 1 missed day due to Thanksgiving

12/30/85: Anita Gillette, Dick Cavett - 1 missed day due to New Year's Eve

6/30/86: Jo Anne Worley, Nipsey Russell - 1 missed day due to July 4th programming

The Vicki Lawrence/Henry Polic II session was week 202. Multiply that by 5 days a week, and that's 1,010 episodes. If we're going by the premise that the Conn/Gilliland week had four days, taking it with the other nine skipped episodes above, then we subtract 10 from the 1,010 and end up with the Friday show of the Lawrence/Polic week being #1,000. If the Conn/Gilliland week had only three days, though, we now subtract 11 from 1010, which leaves us with 999.

USA skipped the Conn/Gilliland week of reruns in the spring of 1992, so I don't know for sure how many episodes there were that week. (Sometime early in the '90s, USA had a change of policy regarding "Pyramid": If that week of reruns didn't have five full days, they just skipped it, whereas earlier in the run, they showed the partial week and filled the gaps with episodes from another week.) I don't have the TV Guide from this week, but I could check the microfilm the next time I'm visiting my alma mater. That might solve this mathematical puzzle.

Hope to have an answer for you (and myself) soon!

Brendan