Earlier years used a date code letter for year. If you look at those 68 340 tags they are much different in lettering on tag than other tags like the 4013. 38th week of 64 works for a 65 model. I am sure there are some made earlier and others later. As long as no "S" not a service distributor. I may have a 340 distributor tag. I will need to look at it. But the first 2 tags you show are unique with that embossed prestolite limited for 1968.
From some older jeep documents and such the letter code for year would have to repeat going back from the autolite days to the prestolite.

This the early 60s letter codes I believe are correct:
R = 60
S=61
T=62
U=63
V=Not used Corrected
W=64

There was no plant code. On the early ones it was month year. 5 R May 65.
Later it was 3 numbers and week year. Transition period????