So it is interesting after doing some research on the 340 distributor. It does look like it used that unique tag from the examples I seen. I would add the IBS numbers to your list as the letter code after the 4015 helps with model year too. From you list I would say:
Z=67
A=68
B=69
Also, the 4015C 3438317 is the early 1970 distributor. The later version 4018 retains the 3438317 chrysler number but has the different IBS number as I mentioned. I would believe the number in your list is a month. Why they did this for the 340 distributor, when all the other IBS around that time was in a new format with different tag logo is beyond my knowledge.
I learned something new today.
Glad we had this discussion, because I learned something new too - my calendar posted above originally had an error that I was able to fix, and now the date codes on these Prestolite tags make sense.
Another error that needs to be corrected is concerning the photos I posted above on 06/17/22 of the 1968 340 auto distributor with the Prestolite tag damaged on the right side. The text says "The seller says the date code is 8B", but this cannot be true since B = 1969 and it is a 1968 distributor. I say the illegible month/year code must be either 8Z or 8A. I think I see part of a Z in the photo.
Being able to fix this error helps prove that the calendar above is correct.
