What you've found is correct. Lifetime Maps [LM] can only be purchased for the region originally loaded to the unit so only 'one-off' NA can be purchased from Garmin for your EU localised zumo without any additional files such as JCV. There are some minor exceptions such as units with USA only mapping can have LM for all NA added but that's only because Garmin doesn't offer USA only as LM. There were also some rare units in the past often called 'transcontinental' or something that had both NA & EU loaded as OEM but as non-LM. For those you can purchase LM for both but you wouldn't nowdays because of the cost involved, as it'd be as cheap or cheaper to just buy a separate device anyway.
Or, you can go to the NA map threads and get it all for nix/nada/zilch/nuttin' .... [Only registered and activated users can see links. ]