Do you know what validation means in that context? Not to be glib, but "validation" and "verification" and "certification" are not common language in those contexts and have fairly precise meanings. It does not mean they will perform the test again, and in practice probably means they will review the activities in the certification with the assumption that "qualified persons" planned and conducted it. Essentially, an agreement that the FAA was competent and trustworthy with minimal checks to ensure that was the case. That has actually been historically very reasonable and sensible, and this is a rebuke to the FAA from the EASA. It will raise costs and time for US airframes to get to EU markets, which essentially means globally.
edit: not precisely my area of expertise, so corrections welcomed
edit: not precisely my area of expertise, so corrections welcomed