I know nothing about coins but even I heard about this......

"If the grading service got a box from a distributor, they could not tell were the coins were produced."

The graders got a box of 10,000 from West Point, it was well documented at the time.
Coins struck at the Philadelphia Mint in 2015 had various 5 digit serial numbers beginning with 1, while coins struck at West Point had 6 digit serial numbers starting with 1, 2 or 3.