To watch an NBA game is like a life objective I have, and you say that eheheh
Well... Personal opinion: I would rather watch college basketball games over NBA. You can still see great plays, but in college they play a lot of defense too, also there is quite a bit of "nba talent" in the college basketball.
You see more than 1 off rebound from ft in college too....
Just saying that 1-7 kinda percentage that it happens sounds about right. Frankly you probably think it's rare because in general a missed ft is rare compared to a make... And you can only rebound the final ft shot anyways. So it's rare for 7+ opportunities of it to happen in a single game.