Ok, I have an Etrex 20!

I have 11Gb of Topo maps on the SD card. If I put all the maps in the GARMIN folder then some maps disappear due to the tile limit, ok!

So on the SD card I created another folder called EXTRAS and moved all the non essential map img's there.

As Etrex 20 only sees the Garmin folder, then the other maps are ignored as if they are not there!

But they are still there ready to be swapped between these folders when needed in a flash.

Another folder for extra maps seems to beat the tile limit.