The 13 was the plug gauge that would fit the bore. The 13-1 wouldn't go in. I think I'm remembering right that 13 is .719. The .722 is still in proof , but the .729 must have been honed/reamed cleaned up and is now slightly out of proof. With adequate wall thickness, not an issue. There was so much variation in tooling at that period the variations of dimensions was really large.