There was actually a theory by someone, whose name I don't recall, that claimed that all descendants of Queen Alexandra were actually exempt precisely for that reason. Have the courts ever ruled on the matter ?
Certainly, on a strict reading of the text of the RMA, there are grounds to argue that.
Yes, this strict reading was known as the Farran exemption, after Charles Farran, who in the 1950s wrote that the BRF was no longer bound by the RMA because of Queen Alexandra. That interpretation was ignored.