I've got two rMBPs from 2012, one is 15" (with the infamous LG display, retentiongate anyone?), the other is 13". 15" is heavy used and has some marks from the keyboard on screen, but coating is intact. 13"'s screen is in nearly perfect state.

No "staingate" at all. Sure, there are many other gates like magsafecrapgate, yosemiteslowgate, unbearablyslowgraphicsgate and such. But no staingate.