Hi ya Chris. Whilst I cannot with all certainty answer your question, I can provide a research project for you, and a bit of hobby history.
First, notice the Mantle in question does not have the many die-cut tabs that usually circumvent Dan-Dees. However, research this: several New York area ballplayers were put in the set. Do a search on eBay and the PSA and even SGC set registries for anyone submitting photos of their Dan-Dees. Remember to look for set as well as individual player registries. The point to decipher: are the die-cut tabs to be found on the New York Dan-Dees? I cannot positively say that I recall the tabs are also on the Yankees, Dodgers and Giants, as well as the one Cardinal, Red Schoendienst. Milprint may have decided to add them after their initial run of Cleveland and Pittsburgh players. The Indians and Pirates were die-cut; the others may have been cut by the printers in a different manner.
Second, as to the no gloss aspect of this card, remember, the paraffin coating on the Dan-Dees does not leave them very glossy; rather, an elegant semi-gloss. Furthermore, there were known to be several collectors during the 70s who did not appreciate the paraffin coating on the Dan-Dees. Therefore, they would CAREFULLY REMOVE as much of the coating as they could, usually with one of their wife's worn nylon stockings. One of those collectors was future Rare Sportsfilms founder, Doak Ewing, who pretty much introduced me to the Dan-Dees in about 1975. He always removed the paraffin coating. No big deal, as the coating was known to catch (a la flypaper) all sorts of dust, specks, and potato chip bits and grease. In many ways, a most legitimate manner of cleaning the card up.
Third, notice the potato chip stains on the card. A major clue, this. Makes for undeniable proof that the card originally resided in a bag with the Dan-Dee chips--whereby one day long ago it was plucked out as a youngster's free prize for buying those delicious Dan-Dee Potato Chips. Therefore, this vendor is totally incorrect in labeling it as a proof card.
Save your hard-earned money, or easy money, for something better. Take care, my fellow collecting warrior.
--Brian Powell