If you ask IMDRF folks, they will say that they are not totally relevant because they won?t be updated anymore.
But even IMDRF documents do use some concepts from old GHTF documents.
IN another example, we are using several definitions from GHTD in the revision of ISO 13485.
And I just presented last week on theRegistration and Listing document to the Taiwan FDA.
SO yes, they are relevant. Ans this is mainly because they were created as "state of the art" at the time and most of them are still 100% valid in the concepts presented (does not mean that one or any regulations totally following them, but they all generally agree with the concepts).
However, as documents them selves, and due to not being updated anymore, they will loose some of their usefulness in the future (may take some time). And they probably won?t be used in a direct way anymore for regulatory purposes (their primary objective in the past) unless there?s no updated information on the specific subject.