"The genus Naso contains all the unicorn tangs which generally swim in large schools feeding on zooplankton. The exception is Naso literatus, the "lipstick tang", which feeds on algae and usually lives in pairs. Many of the unicorn tangs don't develop horns, and some only develop horns on the male fish."
A quote from another online source. Fishtanker according to this source and my personal experiences I think you are right regarding N. literatus... I thought about this for a little as I've personally seen schools of tangs in the Caribbean, Hawaii, and Galapagos, and always remember seeing the common naso (Naso literatus) in Hawaii only singly or in pairs... interesting to see that this guy is different.
And by the way it was something seeing huge adults in the wild and the size of their scalpels... beautiful fish...
My first introduction was when I was 13 and I got in the water at Hanauma Bay in Hawaii, dropped my head under, and saw a HUGE school of achilles tangs. If you see the way these guys move in the surge zone you'll definately have misgivings about keeing acanthurus species in small tanks... the nasos would just sort of wander around, while the convicts and achilles flew!