I have never seen a stock connecting rod with cylinder numbers stamped on them. Why would they? They are not specific to a cylinder and are all the same. It would require the factory to stock 8 part numbers when one would do. Plus the guys building them in the first place are using new parts so there is no need to keep track of a specific cylinder the a piston rod combo is installed into.
I would have to say some one was in the engine after it was orignally built.