I found John Charles George baptism in 1820 son of John and Mary Ann Knapman, fathers occupation as blacksmith in the Dockyard.???? Mary anns surname is the peculiar spelling Reddicliffe/ft in Liskeard area, so perhaps her relatives came from there.
Still cant find them on 1841, so could have been anywhere, am assuming they married that year, no trace of that either.Perhaps they did not marry, and moving between Liskeard and Plymouth people assumed they had married in the area they had come from.