Essor Prof
Welcome to Numista.
The information after the year line of 1797 “Over-date 1797/6 exists” is just extra information. It means besides the regular 1797 there's also an overdate. There should be an extra year line for the overdate, just like in Krause:
Mintage figures are often not known.
I'm not so sure, that a new year line is needed for all overdates, some are easy and some are very difficult to determine. Extra year lines might be filled in wrong by non-observant members, and then making it difficult to make correct swaps.
Globetrotter
Coin varieties in French:
https://monnaiesetvarietes.numista.com