I recall in the summer of 1973, regular programming was preempted on a network rotating basis, due to the Watergate Hearings. You'd notice that on the very first Match Game '73 episode, Gene Rayburn closes the show saying "join us, next time..." instead of "Tomorrow."
It became quite a custom on CBS shows, at least, where shows like MG, Tattletales, and even during the 79-80 version of Beat the Clock, that the celebs would appear in odd 5-day spans, over the two week blocks, and was usually due to preemption related to news events, or even the monthly CBS feature called IIRC, "Afterschool Special."