"The map is dated to 1763 but is also clearly marked that it is a copy of a map made in 1418..."
I really don't see how that much detail could be in a map made in 1418, even if this guy's discovery was authentic. It's one thing to "discover America," but this guy also apparently discovered the Gulf of Mexico, Hudson Bay, the Ithsmus of Panama, Alaska, the St. Laurence Seaway, the Yukon, the Isle of Catalina, Hawaii, Australia, Europe, the Berring Strait, Africa, the Persian Gulf, the Mediteranian, the Black Sea, Japan, Greenland, Bermuda, India, Antactica, the Phillipines, etc....
And oddly enough, his depiction of his homeland, China, doesn't seem to be as accurate as his depiction of a lot of other places.
See: http://ancientmongolia.com/ . Now, check this: http://images.google.com/images?hl=en&q=stonehead%20indiana&sa=N&tab=wi
The first image was erected somewhere in Mongolia circa 1000 BC. The second image (which has been "maintained and enhanced" by modern artists) was "there", in place, in Story, Indiana, when the first Europeans penetrated the area in or about 1542 (see: DeSoto).
The only well-known spot in North America North of Mexico to find surface "gold" easily is right there at "Stone Head" on Salt Creek. Whenever DeSoto asked the Indians where the gold was, they'd point in the direction of "Stone Head". Even in the Far West, this spot was known.
I'm wondering very seriously now if "Stone Head" at Story, Indiana is a Mongolian "deer stone".
I'd earlier thought this artifact had been carved by the Sa'ami settlers who moved into the area about 1835. But, maybe not.
So, you asked how it is that elements of North America's interior got added to the Ming (Mongol) Dynasty Map used or prepared by Admiral He. Maybe the Ming (Mongol) had that information all alone!