@SKPC thanks for posting the 30+ sernos, on that other thread.
From looking at the partial list so far, I have a few observations, and guesses.
1) For the most part it looks like the 6-digit sequence numbers pre-date the 5-digit sequence numbers,
however,
not including some of the oldest (low-digit) 28" Shelby bikes;
2) For the 6-digit sequence numbers, as the prefix letters increase, so do the sequence numbers; (e.g., K's look to be 100,000 series, and M's look to be 200,000 series).
3) The list does
not have any 5-digit sequence numbers with the "D" or "E" prefixes, perhaps those were during the war, or just
not yet reported(?).
4) It seems that more prefix letters are observed than there are years to account for, indicating perhaps some overlap, or more than one letter used in a single year,
not a 1:1 correlation; (maybe suggesting spring-summer & fall-winter sequences?).
5) Looks like Shelby did skip some letters: O, Q, I, J, and maybe L?
Perhaps Ken Swank's 1997 list might be amended, and used for any parts that might work (post-war?). We have seen a few "G" serial numbers lately, maybe Ken S. got that
one right, at 1945-G(?).
Perhaps the earlier 1930's numbers (6-digits) still need more data collection & analysis.