I may be wrong, but I believe the circled 20 denotes the factory, assembler, or something. I have an old Springfield .22 single shot bolt rifle that has a circled 21 on it; but no model of serial number. I still haven't found much about it. IF, you find out definitely what the circled numbers mean, please, PLEASE, let me know! I believe that someone on one of the other gun-forums said it has something to do with the manufacturing, assembling, or the person testing the gun before it left; or maybe the person making/testing/ assembling the barrel?