Lorraine, I have a private copy of Maughold burials, transcribed fully in date order from the original parish registers, and I can't see any "RIE" there. He possibly missed it out because it had no name, if it were a clearly separate comment to the previous record.

You wrote "In the Maughold parish burial register next to Robert & Isabella's information the next line down is a listing stating Marker RIE on it...", but you didn't give the date(s) for Robert & Isabella. Are you saying that their burials were together - recorded at the same time?

Sue