I have two sets of UL and two sets of UC as well as a set of 76 (20 mm) end links for champion bracelets. I have been looking for a UP end link (I already have one). They are just impossible to find ! I am surprised someone has not started making pattern end link for UG like they do for other brands.parts ...
The earliest advertisement I can find featuring a UG watch on a bracelet is the Polerouter Sub, circa 1961:
Here is a Polerouter Sub reference 20369/1 on a GF bracelet from the second quarter of 1962. As we might have guessed, these 22 mm end links, the earliest GF end links made for UG, were stamped with a simple “U.” (At the time, there were no other UG end links to distinguish them from.)