Two possibilities come to mind with regards to R.B.14. First, the Royal Navy operated a grid system for the North Sea which was encoded, so it might be an area of sea, but it could be a misprint also, and may refer to F.B.14, F.B. being one of the designators used for patrol units, usually consisting of two or three boats. So it could just be the unit it was assigned to on that night.
I'm still working on the Nore material and will send it you later this week. There are hand written digests held in the National Archives which note activities and patrols for each night — Coastal Forces Logs
— of which I have quite a few, but I don't have May 1942, if that exists.