Yup...it can happen anywhere. Remember, it doesn't matter what the odds were at the time of the ticket purchase so long as the upgrade actually goes through. So just because you believe you have better odds seeing Z3 doesn't mean the Z0 flight won't have one of these events. And since the odds of that evenly distributed event happening are, well, evenly distributed, suggesting that the customer booking Z3 versus Z0 is going to have a better chance of upgrades based on this occurrence is simply wrong.

If I have a "75% chance" (based on whatever crazy metrics someone comes up with based on the minimal data available) to get the upgrade and I don't clear that doesn't do much good versus the 25% chance which does clear. And the truth is we simply don't have the data to say with any reliability more than a couple days out whether odds of clearing one flight versus another look good or not.
Not in this case. They all sign their real names.