The paste does not work if a calf is still with it's Mom. She might lick it off. We had a set of twin calves where they got very sick, and pulled the one with horns and bottle fed it. We used paste on it and it worked well. The other one was polled anyways.
In reality scurs are not a poor dehorning job. They are incompletely attached horns - like growths, usually only attached to the skin, although with age they can eventually become attached to the skull, apparently that happens more on bulls than cows. They are not horns and are not considered horns - in fact, only polled cattle can have scurs. They are also not removed. That way everyone can see that the animal is scurred and not horned. Big difference when breeding for polled cattle. Although some scurs can grow pretty long, most are only a couple of inches big or even just buttons. They are also sex linked - like color blindness in people. A male only needs one gene to show scurs, a cow needs to have both genes to display it. Horns are recessive, meaning a cow has to have both genes to grow them.
If you see those little lumps on a cows/ calf's head, see if they move. If they do, they are scurs. If they don't move, they are horns. ~Jan