It wasn't me that mentioned using local anesthetics for dockings. My vet doesn't use any except in one case with a small one I had that went over the recommended window for doing it.
Here's a link to some info about tail dockings and pain. It is old research but don't hink it's been proven invalid. It is interesting to see how animals are classified by the author. I had never seen that perspective before.
Tail Docking - The Fritsch Report