There is no cap on crimson engrams. Also the sparrow obtained from crimson doubles is not the Same sparrow from the engrams. From the PvP matches you have the chance to get either: 1 crimson days shader per match (if nothing else) 1 crimson engram per match (whose contents will not be duplicates) or 1 exotic sparrow (which I believe is called undeterred) The exotic sparrow from the engram is called undefeated I have yet to get any duplicates and I have opened like 8 or so crimson engrams.