A small number of guitars produced had serials preceeded by a letter, but as to what the letter inidicated is yet a mystery and one can only guess without concrete evidence.
Nearly all guitars produced by Matsumoku (beginning sometime late 1976 or early 1977) bore serial numbers indicating the year and possibly production sequence. Single coil trapezoid face = mid to late 1960s, P-90 sized single and dual coil pickups = early 1970s, normal humbuckers and more strat like singles = early to mid 1970s. When dating these guitars only ballpark ranges is possible. Serial numbers on these guitars were arbitrary numbers and did not indicate date of manufacture. After Arai joined forces with Matsumoku, the serial numbers began to have some bearing on the guitar's production year and rank in production sequence. Unfortunately the number was arbitrary and had little to do with when the guitar was produced. Most guitars produced by Arai such as the Aria Diamonds (not to be confused with the Aria Pro II Diamonds), Lyle, Conrad, Maxi-Tone, Japanese Epiphone, Univox, and the other pre-1976 guitars often had serial numbers usually on the neck plate (I imagine so dealers could track warranty, etc.). Serial numbers for these guitars is not a perfect science, but in nearly all cases after Matsumoku's involvement they can be trusted to indicate what year the guitar was produced.
