Charley,
I don't have any clear pictures right now as I'm rebuilding the computer that all my good reference pics are on. I dug up these two for now and will try to explain what I learned from Mike Thorpe (rszmjt) on the subject of factory issued derby caps. He's handled thousands of these caps and has been checking them since the 1970's for differences between them.
The parts numbers most know for these are 3925801 or 3925805 but they both differ by time frame issued and were also remade by various manufacturers under GM. The early factory originals for 1969 have a double casting rib (or flute) where the screws from the backside of the rings secure to the caps on each of the 4 screw locations. Original production line installed rally wheel caps have this double rib inside, have the GM part number 3925805 and also say made in Canada inside the cap. I think they were made by McKinnon Industries for GM but not positive on that one?
The later versions have a single casting rib (or flute) with one of the above part numbers and in the last 15 years or so, the part number had disappeared completely. They also have various casting flash differences from the factory issued caps or the early over the counter parts but are easy to spot from originals. Below are a couple pictures that simply address the casting ribs, but do not go into the comparisons of the outer fonts and such. I have also been told that 68 and 69 caps differ from each other on the outer beveled edges of the rings where one is more rounded than the other and that the 69 has more pronounced flat edges with a sharper radius.
The later 3925805 part numbers differ widely in the casting flash inside the caps from what is obviously different vendors for GM. They also have different fonts and ring sizes on the outside cap as I have come to learn but still don't know enough about that. I have had 2 sets of originals including a 68 driver with factory issued derby's with the double ribs and made in Canada markings, but quality was poor. Here are two pics showing an original (first pic) and a later cap obviously from GM parts suppliers with the single rib (flute) and various other casting flash markings inside the cap.
Factory (late) issued cap with clean casting inside cap but no Made in Canada markings.
Later cap with single rib and likely an over the counter GM part. Notice additional casting flash.