as for manuals how many people keep their Haynes manual after they sell the car.

Oh dear, I’m afraid I do.
Somewhere I’ve got the maker’s service manual for the van that doubled as a family car in the 1960s. There are only three or four survivors in the UK, one of whom is local and I know its owner slightly.
Spoke to him on the phone a few weeks back. Guess what? He’s already got a copy of the workshop manual.
So it’s still sitting in a bookcase. It’ll still be there in 20 years, I reckon.
*sigh*