Ryan, here are some of my thoughts. Like you i have seen dogs hunt hard dead tired, and on poor food, and every thing else stacked against them, but they arent usually as good as usual. I also agree that every dog will have an unexplainable bad day here or there. But i have seen huge differences in performance just from different feed. Every so often I run out of feed for my hounds, and have to feed the cheep stuff we feed the house dogs for a few days. After four days of feeding junk food, it takes a quick toll on the hounds. They wont perform as well, and will take longer to bounce back after a hard hunt.
Stress is also another factor. I see a big difference in performance when the hounds dont sleep well, get stressed out, or have too much excitement before a hunt.
Another thing would be climate change. They adjust to the climate at home, and if there is an extreem change to climate it can also affect them.
Most of these things are pretty subtle, but still there. I know that most of this seems unusual, or maybe some of you dont think you would ever experience these things, but we all can and will.
For you guys out west, if you live in lower elevation, and decide to take a trip up the mountain to call some yotes, well you will probably have a pretty quick climate change. Or if you are like me and get a wild hare and drive 6it hours north at midnight to run on fresh snow in the morning.lol
Also stress and excitement. If your decoy dog is also a house dog, and you have Christmas dinner at your house. The kids are running all over, its noisy and bussy, then after dinner you decide to take the father in law out to see some decoy action. If you dont think all the excitement is going to affect your dog even a little i think your crazy.
Like i said, most differences are probably pretty unnoticeable, but the small differences could make the difference.