Oh the continuing saga of the numista rarity rating. It's just how many members own the coin rather than a true gauge of how rare the coin is. Because this is a French website the values for the French coins are out of proportion. Take this coin for an example
https://en.numista.com/catalogue/pieces2090.html You'd think that an early 1800s French silver would be reasonably rare. But because there are so many French members it has a ridiculously low rarity rating of 48. I've only seen one listed for sale over here in New Zealand and I bought it.