Well, I’m glad to inform you that just because you’ve not heard it does not mean that it doesn’t happen. I know I had a reply sometime way back when that I’m trying to find where I had linked up a large swath of reverted sanctions - but just in trying to find it, I do have some instances to back what I’m saying. Mind you this is just a small smattering of cases, but the CS forum has time and time again seen sanctions lessened and overturned over the years.
Heck, even when large banwaves go out, if there is some instance of there being an error in that banwave - Blizzard themselves have admitted that there was a hiccup with the data given over and that there would be reverted bans/lessened sentences and the like.
So just because you have never heard it, does not mean that it doesn’t happen.