Here's a photo from Password's 2000th episode, which according to the back of this press photo aired February 29, 1972:
http://tinyurl.com/9xf6x65They must be incorporating the primetime/Sunday afternoon episodes in the count, because after seeing this photo on Aaron Handy's site I assumed it was from ca. December 1972, which would be more accurate if they had counted only daytime episodes. Also, the press description indicates that Pat Carroll and Roddy McDowall were the celebs, even though TV Guide apparently listed Anne Francis and Arte Johnson for that week:
http://abcpassword.tvheaven.com/ABCPass_CelebArchives/1972.htmlPat Carroll doesn't appear in the listings until the week of March 6, McDowall not until the week of April 17. It could've been a one-shot special appearance for both during the 2000th show, but we'll probably never know unless the production records for this run of Password still exist.