when I was running our Malaysian NT, we had a player whose stats went way over his Star potential.
It took forever for a pop, but he did pop eventually. I also have another American friend who was training for a PS pop on his PG for over 9 weeks, but he did eventually pop.
It's a small sample size, but take what you will from it.
I'm sharing an opinion, and what I've seen/ heard / read. Not concrete facts.