I think all the associated files need to be present as well for the map to show up in practice. So if the map needs certain texture files, etc, they must be in the right folders and not still in the cache.
I have this problem too. Some of the maps that I've culled out of the cache folder and some that I've downloaded and installed from other sources don't appear in the list of maps in practice mode or under "host a game".
I could understand that maps that I've culled out of the cache might need files that I didn't transfer from there, though I do have some doubts too, but maps that I've downloaded should have all the necessary files included.
If this were the case, that some file(s) were missing, which are needed by certain maps, how is it possible to determine which files are needed by which maps?
The system seams to be able to find this out rather quickly.