Either of those map types will work flawlessly in modern Nuvis such as both your 3770 and your friend's 40. It's just that there is no such thing as a JCV file for the EU [non-unicode] map that will work in the x0 but there is for the 37x0. But for the EUU [unicode] map there are jcv files specific for both models.
Sorry for any confusion caused by my mixing up the 2 links and thx to Loly for sorting it out.