It doesn't matter whether it's 50 years (Myra), 70 years (Adolf) or 2,500 years (Jocasta). If the only context in which anyone has ever heard the name is memorably nasty then that's what will stick. Adolf will not be OK for a British child in 2040, or indeed 2140. Nero or Caligula will never be charming names for baby boys.
Fred and Rose by contrast remain absolutely fine for babies, regardless of the Wests (though perhaps not for siblings) because most people can think of loads of other people with that name.