I'm a bit confused. How did you "uninstall" the maps from your computer? You can't just delete the files, that may create some problems. Most gpsfiledepot maps use Garmin's old format where the Windows registry contains important information that is needed for each map. If you delete the files, the registry data will still be there and will probably confuse Basecamp/Mapsource.
Garmin no longer uses this old format, but most people here do. The new format (gmap) does not use the registry. Each map should include an uninstaller that takes care of removing all the files and registry keys. It should be in the same folder as the map files, you can just double-click to run it. Should also be able to uninstall from the Programs control panel in Windows 7. Don't have any maps installed on my Windows 10 machine yet, but I assume the uninstaller would be in the Apps settings.
Alternately, use the program I mentioned earlier. It can uninstall maps for you. This is probably the easiest way:
https://www.javawa.nl/gmtk_en.htmlJust to understand... do you want to uninstall the map from your computer, but still be able to access it in Basecamp when the GPS is connected, like a "real" Garmin map? GPSFileDepot maps typically can't do that. But that other Javawa program can do this. There is a option called something like "visible in Basecamp" that you can set for each map with that program.
https://www.javawa.nl/jdm_en.htmlOne other thing - if you use Mapsource to transfer maps, the file will always be named gmapsupp.img. Therefore, a new map will automatically delete the previous one you installed. You must manually change the filename to prevent that. For example, after sending with Mapsource, change the name of the gmapsupp.img file to michiganTopo.img (or anything you want). Then repeat this for each map you send to the gps.