I also experimented a bit with my Oregon600 and the Topo Norway Experience maps.
Experiment with other Experience maps no problem, but with the Finmark map (nr. 10):
On SD card I can see the map but no trails to select (*.db on SD or internal, no difference).
Map + db internal on the gps: I see map and can select trails. (I use demo-mode and select via the satellitee-screen a new position on the selected map).
When I have another Experience map(s) on my GPS (and even turned off): I do not see the Finmark on my GPS, is not part off the map selection. (Basecamp sees the Finmark map and the other Experience maps, also JaVaWa Device Manager).
So, Further research should be done for the Finmark map I guess.