I compile a Garmin map and install it in Basecamp. I then use Basecamp to install onto the MicroSD card of a Garmin Oregon where it appears as Garmin/gmapsupp.img.
If I now copy that MicroSD card is there any reason why the copies should not work in other Garmin devices (assuming, of course, the card size is supported by the firmware)?
There might be an issue with the Nuvi and the new "Drive" series. These units expect maps to be in a folder named Map instead of Garmin. I have not tried this for a long time, but I remember when they made the switch, I think I had a Nuvi 1350 at the time. I seem to recall it ignored maps in the Garmin folder. But I also recall the behavior was different on internal memory vs SD card.
This might have changed recently. Will try to give it a test on my Nuvi 3550 and Dezl 760 if I get a chance. If they need to be in the Map folder, you could actually use that to your advantage, and put separate maps in the Garmin and Map folder, and each could have a custom .typ file to make it look best on the different devices.
I think file \Garmin\gmapsupp.img on SD should always work.