The other thing I'd add is lots of times you wouldn't even know right? If you're not at the gate and they call you, you might've missed it. If the gate agent looks at the situation and just says "upgrade the couple, it makes more sense", you'd have no way of knowing they got upgraded over you unless maybe afterwards there was something in expertflyer (I'm not an expert on it, so I'm not sure EXACTLY what it shows). There's always the possibility too that they upgrade the SE and someone else at random. Employees often get this as well, don't forget about them thrown in the mix.