Hi, Long time lurker, 1st time poster. I'm appealing to those who have a more thorough knowledge of the factory markings on the bodies of our beloved pieces of wood. The circular stamps that appear on the bodies of some Tele's (mine included). See picture below (not my gee-tar, apologies to the owner!) What do they signify? What date range were they used? Anything significant about them? Any help greatly appreciated. Regards, Chris.