I was wondering if anyone who is a whiz with Fuji serial numbers might be able to help me out.... According to the information that they have over on Classic Fuji and in a much earlier thread here, the normal serial number pattern for the mid 1970's would be:

YYXZZZZZ

YY = Last two digits of the year
X = Letter indicating the month of production
ZZZZZ = Individual frame number

The general consensus seems to be that the individual frame number is the sequential number of that given model made during the month in question. Thus 76A12345 would be the 12345th Fuji "whatever" made during January 76, 76B00123 would be the 123rd Fuji "whatever" made during February, and so on.

Looking around at the few other examples of the high-end / hand built Fujis from the era, I'm noticing a pattern wherein the first number after the month code is either a "5" or a "0" - e.g. 75A00012 or 75A50012. With some of these bikes, the manufacture of 50000+ in even a year seems highly unlikely, let alone per month. Thus, I'm wondering if the "5" means something else, and if so, what?

Granted my sample set is pretty small, so examples to the contrary would be welcome.