Correct in the case of map split on your device. The map on your device is split into 2, that is a recent change to the US map, it's been normal with the EU map for a while. The reason is that the map is now so large that it exceeds the FAT32 limit of 4Gb. Your computer has no such restriction so when Express is used to install the map to your PC it's installed as one map and not split.
No, BaseCamp does not make a distinguish between the different maps of the same version in the drop down menu.
If you click on the Maps menu it will tell you which map is intalled and which are on the device. You can also see which is selected as well as change the selection.
For the device versions, you'll probably have to zoom in and switch between the two and see which proviides the most detail.
I did make an error in an earlier post. When you are out of the coverage area of the selected map you see the global map, but you still access the data (POI etc) associated with the selected map.
