The MDR, Annex XIV, 3, indent 3 states:
"Clinical: the device is used for the same clinical condition or purpose, including similar severity and stage of disease, at the same site in the body, in a similar population, including as regards age, anatomy and physiology; has the same kind of user; has similar relevant critical performance in view of the expected clinical effect for a specific intended purpose. "
As long as the data the manufacturer already has meets the required level of rigour and you're able to demonstrate the population is similar, then there should be no issue with using any existing clinical evaluation data they have from use in another market as part of the registration process and conformity assessment under the new regulation within the EU. I'd suggest something along the lines of a "User Profile Assessment," with possibly a comparison of age related, anatomical and physiological profiles of the population of their existing market against the demographic within the EU market.