Originally Posted by 63rickert

I think I see that hole in the dropout also. That is for the Campagnolo Sportman (1961) derailleur. Which would not likely have been used on this bike, the dropout is simply ready for it. There are a lot more of those dropouts than there ever were Sportman derailleurs. And the hole was even there before the derailleur was finally ready to go. Dating indicators are not perfect.