Heater instrument panel differences for 67?

My 67 Dart GT was made on Dec 5th of 66 and it has a spring on the left and right hinge. The left one wore unevenly and basically oversized the rotating pin and it closed cockeyed. I have a suspicion thats why they went to one spring
Interesting.

I have a 11/66 build 67 Dart GT and 2/67 build 67 Dart GT both only have one spring. Go figure?