Always_Ask_Questions,
“Still, you can look at a variety of cases and get a feeling when a case is a stretch case or reasonably a norm – in the latter case, it is discussed in many situations, with practical details. “
A category can be rare to occur in practice, but highly complicated halachically and thus require considerable discussion.
“Also, a notion that a man should not live/visit too long at his in-laws before of mother-in-law there. This hints that husband and bride’s mother are typically close to each other in age.”
No it doesn’t.