Any of these combinations will work:
1. Maps as traditional name (gmapprom.img etc) in unit's .system folder, with corresponding .jcv files in sub-folder JVC of unit's .system folder.
2. Multiple maps as 'anyname'.img in Map folder in unit's root, with .jcv files as 1.
3. Map as gmapsupp.img in Garmin folder of sd card's root, with .jcv file in sub-folder JCV of Garmin folder.
4. Multiple maps as 'anyname'.img in Map folder in sd card's root, with .jcv files as 3.

Note that *.jcv files are specific for each map release. Having outdated files for earlier releases of the same map series in the same directory can cause problems. However, having multiple jcv files for different series maps in the same folder is fine.