1974 Bucket Seat Question

Hello. I have a line on a 74 dart with white bucket seats. High backs. They are just like the ones in the picture I am attaching.
The question....
They have the hard backs not the soft backs. What year did they stop using the hard backs?
I thought 72 was the last year of the hard backs. I dont have pics of the ones im asking about, but the interior is all white and matches the wear and tear. They are pretty trashed but still rebuildable. I figured they were worth about $75-$100 per seat. Sound about right?
Thanks for the education.

1974 dodge dart sport&bonjovi 179.jpg