Not sure what Model specifically, but the XD series have had a few changes. One change was the change in the black finish to melonite, the other was the relief notches in the locking block. The older ones could crack.
Also, the older .45 mags have also been updated due to cracking on the back @ the top
But the 45acp models have all had melonite so no worries there. And I wanna say that all 45acp models came with the updated locking block. I got one of the first 300 sent out as gifts before they shipped to the stores and it has the relief cuts. The day before I got back from that years Shot Show it was already at my door step.
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