What were IF code wheels used for?

[Thomas]

The later IF coded wheels could be different from the earlier, 1969, dated ones, as later XT coded wheels are different from the 1969 version.

I have had a set of 1969 dated IFs and XTs side by side and there was no obvious difference.

I have also had a '69 dated XT beside a later (I cannot remember the exact date) XT and there was a difference in the design of the center, where it is welded to the outside of the rim.

I wish I had taken pics, but it was when I back in the mid '90s when most people did not care.