Here's some information that I got from a friend who talked to Santana 5 years ago.

Serial number is 5 digits long.

1st digit is model year. "X"=2000, "Y" =2001, etc. (no letter "O")

2nd digit is frame material. "T"=titanium, "K"=TeamAl, etc.

3rd digit is frame size. 2/3=sm. 4/6=med. 7/8=lg. 9=xlg

4th&5th digit is serial number. "01"=first one built that year.

To verify, give Santana a call. They are very friendly.