I bought a Vittoro 531 in a charity shop in bury st edmunds suffolk for 20 quid ,it was a bit beat up but I`ve cleaned it up and put Martin M1400 Marquis Acoustic Folk Guitar Strings on it and it sounds great , can anybody tell me how you can get the age of the instument , is the "531" reference something to do with the age?? any info would be much appreciated