Not sure I correctly understand the question.Cure firmware was made from old boot and new core 6.10 firmware,using the garmincure3 made the rgn file,updated by updater.exe.
Tried this too.Found:nuvi13xxand14xxseries_regionfileonly__510.gcd 25.5MB that is bigger than nuvi13xxand14xxseries_GCDFile__580.gcd 15.7MB.Updated (downgraded) via SD card,still removable device in my computer....
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