Vantage guitar dating
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.
Many vintage guitar owners value guitar dating and guitar serial number data to date their electric and acoustic guitars.
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.).
Unfortunately the number was arbitrary and had little to do with when the guitar was produced.
Chauntelle Du Pree of the band Eisley used a Lotus Stratocaster copy for many years on tour and to record.
While the quality of this guitar would not typically be considered to be on a professional level, it did provide an inexpensive platform for experimentation and upgrade (with non-Lotus parts), which resulted in a unique sounding instrument.