What were IF code wheels used for?

[travlnz28]

The link that Eddie posted from Team Camaro has some good information on the differences in the wheels. I have a very early IF that is 1968 dated but has no date code next to the valve stem hole. It has large ND in the front center. I have 2 November 1968 wheels that have the date code next to the valve stem hole and seem to be by a different manufacturer since there is no ND in the center. Cosmetically they are identical. I have another IF that has a late 1969 date that was produced by a third manufacturer. It is different cosmetically, mostly noticeable from the back and the backspace is about 1/16 inch different See picture comparison.

I compared two May, 1969 XT wheels to the IF wheels. The XT's are identical to the November, 1968 IF wheels and are the same manufacturer with the same fonts used for the markings at the valve stem hole.

If anybody wants any additional info about these I'd be glad to do what I can.