I was just thinking today, what became of episodes which for whatever reason never aired due to being pre-empted unexpectedly such as the episode scheduled for 9/11/01 or the week following or even more recently episodes that were pre-empted for the impeachment hearings? Are these episodes just stuck back in the rotation and the producers just account for having them available and reduce the taping schedule later on to compensate, or are they just lost forever?
Regarding 9/11 specifically, the summer reruns were still underway when that happened, so there wasn't a new episode
to pre-empt. The entire new network TV season got pushed back a week in the aftermath, though, and that included TPIR. They shuffled a few episodes around I don't think I ever knew, but the most notable change was that the entire third week of the season got shifted to January, presumably so that they could leave as many episodes as possible when they'd originally planned to air them. (They also then shifted that week's Thursday show
back to October in place of the second week's Thursday show, presumably because the former had the debut of Pass the Buck on it.)
Pre-empted episodes all get aired. If they're only partially pre-empted, they might not get aired in their entirety in every timezone (and some parts occasionally don't get aired in
any timezone), because they're never guaranteed to be rerun, but they
do get broadcast. Outside of a small number of shows that were intentionally pulled because of severe production errors, the only episode that's never been aired at all is September 14, 1978, a half-hour episode that was taped in anticipation of a magazine show pre-empting the first half of Price's time slot that day that ended up not being needed.
As for cutting the taping schedule, things don't work that way now, but it looks like they did in the past. Up through Season 26, the show just appears to have done however many episodes it could fit in before the second or third week of June. Starting in 27, it changed to a straight 175 shows per season (28 and 29 have fewer because of Bob's surgery in 1999 and some weirdness involving the first two weeks of shows taped under 29's contract being regarded as part of 28), and it was upped to 190 when Drew took over in 36.