If it has the modern eight-digit numbering system, in use since 1977, then you can get the day of manufacture as follows:
ABBBACCC
AA = the year
BBB = day of the year
CCC = depending on whether it was made in Kalamazoo Michigan, or Nashville Tennessee (or Bozeman Montana, but I think they only make acoustics there), the number of the instrument made that day.
So for example:
90319604
Year is 99
Day of manufacture is 031 - January 31st
It was the 103rd guitar made in Nashville on that day (they start the numbers in Nashville at 501 - or maybe at 500, and it would be the 104th made that day?)
If this is too confusing, post the serial number here and I'll decipher it for you.
Hope this helps,
foo