Not to diminish any experience on the matter you may have but it's Extremely unlikely you actually introduced velvet. The regal would have been dead once a week. You're not going to out feed velvet. It's not going to bounce about then disappear.Not on purpose, I bought a coral from a tank that had velvet, according to many on here and elsewhere it’s said that coral can’t bring velvet/ick with them, well… surprise surprise coral will bring disease into a tank! Not lost a single fish to it, they just got a few spots for a few days and den it was gone, the regal tang, coper band butterfly, wrasse and the chromis got sold to the lfs this summer, the clowns still with me from the downgrade. The ccb and the regal was iconic at the lfs as they never seen such a fat fish in they’re time in the trade.
Edit: I did had a make up quarantine at hand at the time(if needed). It was just not needed in my case, the place were the coral come from I later found out that it had all his fish wiped out by the exception of one.
When the spot you got it from brought velvet In, they likely had ick in there already and was under management. Luckily you only brought ick home or your story would be much different.