Actually, I think only 4 of them are upper, the lower ones are from the bottom jaw. I have noticed that sometimes with the different "species" of predators there are sometimes differences in the teeth. I can't remember if the Elder has 4 top teeth in the movie though.
Yep, it does have 8 total inner teeth, but that's pretty common. I've got a pretty good collection of alien/predator comic art collection books and I've noticed that the finer details of the characters are changed on particular artist's discretion.