I know I sound like a broken record (for those under 40, look it up

): Apple doesn’t do their software development on an ad hoc basis. If they intend to release an 18.2.1 before the holidays and vacation time, then they put it on the schedule and got the necessary work done before people leave/left. And you can be sure that if an urgent 18.2.1 were necessary (but not originally programmed to be part of the release cycle), they have a skeleton crew of engineers around who can get it done. And they will call people in if needed (as in a super serious zero day bug).
Large organizations don’t leave stuff like this to chance. It is all meticulously scheduled, working back from when iOS 19 has to be released to manufacturing.