I've suspected this about other figures, and I know that accessories can be factory specific (see Craig T's posts concerning Jedi Luke which he has absolutely cracked the code on). There were a finite number of factories, and it seems reasonable that the same factory could produce an HK COO along with a blank COO of the same family, in the same factory. And, if not, then when the factory producing a blank COO figure got the molds, they perhaps got the die to cut the capes as well. Or, maybe they just got samples to follow. But there is obviously a good deal of wiggle room with these capes, likely because the process is as Bryan explained it. Sort of like trying to cut several pieces of paper at one time.
Granted it is only 3 samples, but the chances of 3 random samples ending up with the same mismatched accessory seems unlikely. What I would love to do is have people contribute data. Obviously that was attempted before, and didn't get very far, though.