I have received the 2 Canon extension tubes EF12II & EF25II. The only writing on the tubes was "1301" on the EF25II and "1201" on the EF12II. So my question are these S/N?
On the box there are several more writings, for the EF25II:
CZ 23522000DB0107
9199A001 [AA]
EAN/JAN 4 960999 204307
UPC 0...