It is a good idea to assume that all CS plates are reproductions. CSA as well. There was a die set for this plate on ebay a while back for $500.00 and many thousands were made for reenactors since the 1960s. The small inner ring is the tip off. The dies were made copying the US plate which had that ring. The CS plates did not. Another tip off is it is in too good a shape to have been buried for over a century and a half. There are other little things but the ring is the big one.