I posted earlier about Estes E15s with a date code of 13X10, with the X being 1993 I think. If 'X' is 1993 that would make 'A' 1970. I have mini motors and B14's, and 1/2A6's with full dates (like 2/27/76) printed on them as late as 1976, with no letter date code on them. So I have two questions if anyone has any idea:

1) What was the first year to use the letter date code?

2) Why wouldn't Estes start the date codes with 'A'?

Thanks for your help!!