I've got a Convict and a Sailfin Tang who sat tank to tank for 3 years. When I finally put them in my large system, there was 0 issue. Been over a year, no issue.
Recently added a Kleini Butterfly fish. Convict Tang did not approve. I expected it so I had the Tang in a big acclimation/isolation box on the side of the tank, got him out and into the sump for a bit. Took my big bathroom mirror and put it on the side of the tank and took the Tang out a few days later and reintroduced to the tank. Spent the last week swimming at himself with the kleini. The past 2 days I've been taking it away for an hour here and there, 0 aggression. I'll Probably leave it for a month or so and see. Anything arises, I'll just swap the Convict out at lfs since he is a big healthy one but a nightmare for me lol