Vanderbilt University has been taping evening news broadcasts, as well as many special reports, since August 1968, and their database of recordings often gives an idea of what was pre-empted for news coverage on a given day.
http://tvnews.vanderbilt.eduOn the day of the Challenger explosion, for example, it looks like the networks broke in at 11:42 a.m. ET to cover the event.* On the TPIR timeline at golden-road.net, there's no indication that any episodes were rescheduled that week or subsequent weeks. (With TPIR, of course, interrupted episodes can always be rerun in full during the summer.)
In the summer of 1973, the Watergate hearings, on days they were held, usually started at 10 a.m. ET, recessed at noon, then resumed at 2 p.m. In practice, they weren't always recessed exactly at noon and/or the commentary lasted into the noon slot. On July 10, 1973, for example, when it was ABC's turn the carry the hearings, their coverage lasted until 12:12 p.m. ET, meaning "Password" was joined in progress. On shows that have a set airing order (unlike TPIR and LMAD, for instance), I would think it would get chaotic to partially air an episode, then re-air the whole episode the next day and a brand new (hopefully uninterrupted) show the day after that. Letting the episodes stand as partially aired would seem to be less of a headache overall, although I don't know what percentage of the show had to be aired for players to get their winnings.
*N.B.: Vanderbilt is in the Central Time zone, so the start/end times in the database will reflect that.
