Hi George,
I'm fairly certain that the change at 7938 was the change from all-red to amber directionals. This was in the 1969 model year. My car had all red at 7262 made in the 3rd week of January, and I know some late[er] '69's had the ambers. Don't know if this had any effect on the Euro versions.
As for the second change, I'm not quite as certain, but I believe that to be either:
a) addition of pigtail or socket to plug in the side markers; some point in production in 1969 they changed from reflector to markers. --or--
b) something to do with one piece/two piece assemblies where the chrome frame is not separable from the lens and backing.
Regarding a) above, it appears on mine as if the ability to plug in the side markers is afforded by the small "harness" that runs between the tail lamps at the back of the trunk; there is a small connector pigtail on each that the marker plugs into. Don't know if my restorer fabricated this or if this is standard. Note that all the stuff is interchangable within reason. I "upgraded" to the side markers and to the amber directionals without a problem.
Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored