Bike pumps (sort of 70's and before) usually were frame mounted onto two brazed points as per this picture:
These pumps were often fitted with a flexible hose that screwed into the business end of the bike pump and attached to the tyre valve.
The item you have there fitted into the same output of air hole that was on these pumps and is sort of the fore-runner of the bike pumps available now that attach directly to the valve.
The bottom end of the Campagnolo part would have been used to mount against the frame, as per newer bike pumps.
Not sure if therefore, you find frames with only one pump mount but guess its possible. As I understand, they are a little sought after.