The latter question cannot currently be answered definitively, since the 1418 map, if it ever existed, has never been found. There are problems with the existing map, however, in that it contains a few anachronisms and is drawn quite differently from other maps out of China One problem is that it is oriented to the North, a distinctly European feature that only became common practice after European sailors began using the North Star for navigation. Many old Chinese maps are oriented South (old European maps were usually oriented East before they changed convention). One explanation is that the map is not an exact copy of the 1418 map, but is a reinterpretation of it.

The former question, was the map really drawn in the 18th century, has yet to be definitively answered. Carbon dating of the paper places it either in the 17th or 18th century. As far as I know, the ink has not yet been tested. There’s some speculation that the map is actually a 19th or 20th century forgery (just written on 17th century paper). So until the ink is tested, there’s no definitive proof that the map was even written when it is claimed to have been.

So while we may eventually verify the period when the map was drawn, the issue will not be settled conclusively unless the 1418 map ever turns up.