Okay, I got it. I agree that the lot of them would not have made sense, I specifically only missed Qui-Gonn. I am also surprised that Qui-Gonn did not appear as a Force Ghost in the saga - but apparantley he didn’t.
It is weird that Force Ghosts didn’t occur for thousands of years of Jedi and Sith activity - but I guess George Lucas really felt the need to explain the origin of everything in the prequels…