I own a set from 1996 that was a handmedown from a school friend.
One thing that I noted was that the bridge of the glasses is straight. I'm not sure if this is still the case.
I would give these an A+ for durability since my friend and her sister before her both played with them as kids and the glasses are still almost newlooking.
I also have a problem with them falling off, but I think this is because the PM #16 they were originally put on had a fatter head than the Mattel #17 who wears them in my house, so they were stretched out a bit.