I am amazed that this mistake has survived as I am very aware of the ease that engraving mistakes can be rectified with a peening tool and judicious striking off. My most favourite restoration engraver had a 'senior' moment when engraving the number on a triggerguard. Thankfully I noticed it as soon as it came back and he had it back to rectify. On the 2nd time round it was absolutely impossible to tell it had been re-cut.
I think it was intentional, maybe for an antipodean? wink