So I looked into this further and the 1971 Duster did not have the square recess for the armrest clips like the 67-69 Cuda's
I didn't check the Dart so not sure about them.
Here's a pic of a 71 door frame and it doesn't have the recesses for the clips, just a hole.
Damm!! Pretty cheezy way to save a few cents!!
View attachment 1716243835
Heres a 68 Cuda door frame showing the slots for the clips.
View attachment 1716243836