The DP traps are awesome. I don't recall ever having the bait stolen but I can see how a mouse could get away with it, but not a crow.
Its been my experience when dealing with coons that however many birds die in a single night is how many coons you have to deal with. However, if you kill everything that kills your chickens, another critter will claim its new territory and the process starts all over. It sounds like you have quite the population of them and the dominant birds are/were in control but now the B team has full range of the area. There may be a C and D team ready when their time comes around.
Bottom line...if you don't secure your birds its only a matter of time.