How do you tell when a Remington Model 514 was made?

I think since most were manufactured before the GCA of 1968 they did'nt have S/N so it's hard to say when they were made. After 1968 they are supposed to have a serial number On the left side of the barrel just forward of the receiver you will find two letters stamped into the steel. With that information we can decipher the date of manufacture.