When you turn on your nuvi, it is normal that it shows 2 different maps with 2 different dates.
Try simularing the route, by turning off the old map (go to tools ->settings -> map -> info).
If it still doesn't work, please write here the following: what is your splash screen? (go to diagnostic menu by pressing the battery icon for 5 sec, press next once, press start test and then more) - look at the number next to Splash. It should be D1340-50.
Next, where did you put the maps? Old map is probably a gmapprom.img in the .System folder. Disable it by renaming it to e.g gmapprom._img and move the new map into the same location, giving it a name gmapprom.img (if you have unl files together with maps, make sure you move them as well).
I assume, you put the correct JCV file into the JCV folder within .System folder. You can also repeat the procedure by putting JCV into Garmin/JCV/JCV file, but keep the old map disabled.
Personally, I keep my map on a SD card, in the Map folder, and JCV is in Garmin folder, also on SD card. Probably if you have map in "Map" folder on your unit, JCV should be in "Garmin/JCV" directory.

I thinks it is highy unprobable, if the splash version is correct that FW version and gupdate.gcd file would affect the outcome.