round vrs. square shoulder -which one is early and when did they change over?

i have a early 73 with square shoulder stem on driver and round shoulder added on passenger. am i correct to assume the driver side square is the correct one?

I am certain that "square" is early. Not certain of when the "round" started. But I think a '73 should be round.

Maybe yours is at the brink of the change. They were near the bottom of the box of the early ones or PO added later one later

Decided to check B. Johnson's book. Outside mirror "was modified for 1972 by altering the mirror size (late ones were wider and shorter) and the angle of the arm. Right side mirrors were fitted in Sweden and an optional convex right side mirror is listed, although it is uncertain when and where they were offered. The nut cages for mounting mirrors were present in all right doors".
Usually right mirrors are simply left mirrors turned around and installed on the right by a previous owner.