Pretty sure you just have the one and if you get an updated version you must replace, you cannot simply add the file to add more onto the previous, yu will need to have it all in one file/folder.
When I uploaded new POI's to my Garmin, it deleted the ones I originally had in there. Why is this?
Keep all your POI files in their original directories on your computer, and just update the new poi files that you want, then use POI loader to load them to your GPS.
POI loader creates ONE file called POI.gpi then sends that to the GPS which has all your updated new files included.
If you only use the new poi files and load them, that is all you will end up with in the GPS..........
All is explained here:
https://www.gps-data-team.com/pda-gps-navigation/topic/3418.html