I wonder if it has to do with Flat luster. I have heard the term used before. Here is the definition from coinfacts. flat luster A subdued type of luster seen on coins struck from worn dies. Often these coins have a gray or otherwise dull color that makes the fields seem even more lackluster.
The term "flat strike" was uses a lot many years ago. It was a catch all for coins struck with worn dies or when the press was not set properly. I can't argue with the 63 grade.
Actually, my main point of contention is PCI calling it a "No P" die error. It is simply a minor grease strike through where the mintmark on the die was clogged.
It's not even what's known as a collector's coin ( made for collecting ) so why would anybody care ......