I wanted to report this issue as well and stumbled onto this old post.
But I want to comment a bit further.
While I don't mind that caches I have found already are shown and I can toggle this on/off on the map, the page actually gives some misleading information.
When I use the Hidden Month for loop 2 and filter on Europe and only caches hidden in 2000 for example, it tells me that there are "5 potential new months (6 caches)".
In reality, I have already found and used 4 of them for the first Jasmer loop, so I can actually only get 2 new months (2 caches) for the second loop.
Is this something that can be changed ?