Looking again at this after 3 years, it seems that this footpath may have been re-routed further north. In particular, see https://overpass-turbo.eu/?w=%22prow_ref%22~%22(^|;)North%20Mymms%20FP%2011(;|$)%22+global&R where overpass turbo is finding FP11 that bypasses RVC to the north. I'm studying this further, thinking that the path near this note is probably no longer valid.