Antiqui Graffiti?

We walked the dog through the woods around Nymans this morning. There is a rocky outcrop from the hillside and its only if you climb up to it that you realise there is a narrow crevice that is just wide enough to squeeze behind. On the walls of the crevice is a lot of graffiti like this, featuring some very old dates. Are they genuine? I don't know, but if they are "WN" was in Sussex carving this as Handel was premiering "The Messiah" in Dublin.