Wow, never thought of that scenario, but I can see it happening. I had the opposite happen to me. One year I had an elk tag and a buck tag. Hunted all day and didn't see much, walked about 8 miles. I was walking back to camp, right at dusk, in a canyon with cloud cover. Walked right up on a young buck (30 yards) with its head down in the sage grazing, I couldn't see it's horns and was thinking "I've got a buck tag so I know that's a doe for sure" when he raised his head up, looked around (I was still as a stone) and then put his head down again, offering a broadside shot with his head in the sage. So then I was thinking "it's almost dark, no way I'll be able to see the sights" but those things just glowed like a beacon, so I got the buck. Not a trophy, but good eating. I don't think I could've made the shot with irons.