My experience varies. Sometimes flight attendants are very strict and monitor the passenger seats multiple times before landing asking people (or helping) people to put their seats up.

In other cases, the final check seems very casual and I see more than one seat partially reclined.

It seems I see the casual attitude on long-haul flights with a fair amount of empty seats. And I have to confess I've forgotten to raise my own seat on occasion without a FA saying anything.