Apple does not typically disclose such things, and I don't recall hearing about them releasing any information. Companies usually don't admit to failed manufacturing processes and by saying they changed the way they make the display panels, that would be an admission of guilt which could hurt them in a class action suit (if there ever was one).
More likely they silently tweaked their manufacturing process some time ago, but there's no way to know this.
Even if the newest models do have the problem, I wouldn't worry about it too much. Apple has formally recognized the problem and have since implemented a repair extension program. In addition, the problem does not render the machine unusable even if it crops up, so critical data and such would be safe even if it were to happen to you.