I will throw this out there... My wife had a cow tag a few years back. We found a herd of 200 scattered in a field in the bottom of the steep canyon. We snuck up as last light was approaching and set up. We watched the elk in the mid thigh high grass and picked on out. We watched it in the rifle scope and my binos as it fed. It took several minutes to clear all the other elk in the back. The entire time it fed with head down only lifting its head for a split second here and there as it jumped to a new patch of food. Finally after a bit the elk cleared and was broadside. My son and daughter both had caught up to us by this time and they were watching this elk feed at 80 yards in front of us. All of us looking, when the shot was taken. The elk spun hard, ran with the herds for 100 yards up the bottom. Then as the herd turned a corner one was falling behind as it turned the corner I thought oh crap that was a spike. But no way my wife and I spent 8-10 minutes watching this elk feed, then my kids both showed up and saw the elk. All 4 of us missed the antlers. The antlers were 5.5" on one side and 7" on the other, still had velvet that was yellow and matched the grass. I have been part of over 150 successful cow elk hunts and this was the only time that this had happened. I have seen other crap happen. Especially on the late season cow hunts near Craig. My wife and I both keep playing it back. There are only 2 options, 1 option is when she finally decided to take her shot she shifted her body and then resettled and in the process ended up on a different elk. Or the other more likely is that we both overlooked the antlers as they were still in velvet and the yellow/light brown color matched the standing grass almost perfect.
It was a learning lesson for us all. We ended up finding the bull. We cleaned him out, punched her tag, packed him out, loaded him in the truck and headed to the CPW office and turned it in. Until that day and that situation I had never been able to understand how a person could kill a "bull" on a cow tag. I always thought the only way it would happen was by flock shooting, taking a rushed shot, etc. But none of that came into play in this case.
When we self reported my wife got an 80 ticket for improper use of tag and was eligible to pay a $5 fee and get hew cow tag revalidated so she could keep hunting. She felt horrible and did not want to hunt, the elk she shot went to a needy family...
Another time I saw it happen but was not part of the hunt was an outfitter client on a neighboring property set up to take a shot. Got a range and adjusted the scope and shot. 6 feet above the cow he was aiming at on a steep hill side was a small 4 point bull. He took the shot at the cow lower and the bull above her was hit right behind the ear. Dropped in his tracks. Somehow his turret was way off and the guy found out that the turret got set to some unreal range and the elk was at like 230 yards. Again not my client and I saw it... I used to hate guys that thought they had a long range set up and were dialing up ranges etc. It was much easier to kill elk with guys who sighted in 2" high at a hundred and held in the middle of the elk.