neohio:
This is also a USMC "Challenge Coin".
As to when yours was dated, we know it was after 1947 (duh) but beyond that--I don't think there were specific varieties that would distinguish in which year the 'coin' was made. I am aware that on some of these coins the year of it being issued to the recipient was shown on the coin--immediately after the 1947 date; like here: