This has happened to me in about one flight in 20. The CC has always been able to fix it one way or the other - with one exception and I got an OpUp to First. Didn't one other frequent flyer threaten to take a box of spanners with him? Incidentally CC can generally fix that slight hump at the end where the seat doesn't quite align with the back rest.

What I now do, at boarding, is test that the seat can go fully flat, since on on another occasion I saw another passenger check their seat and found it maxed out at lounge lizard style. They needed to get an engineer to have a look at it and one happened to be nearby.

The problem is that if you are late to sleep you don't want to cause hassle in the dark to crew and nearby passengers, so it's best to check early.

And if you don't mention it to CC then your line of reasoning to get compo is somewhat constrained....