"The Predators in P1/P2 never had the markings and they were both very experienced." Yes, but only killing humans. Remember that not every Predator has the chance to face an Alien. The group of Predators in AvP were selected and it was considered an honour to them. As i recall, this was a selection of young Predators and so, it could be a recruiting method for a small elite Predator force, an army well prepared to deal with the Aliens extreme threat."The best of the best". Well, that´s how i see it...Cheers