I believe steenei's teeth are much larger, but according to what I've read, when they're juvis their teeth aren't nearly as pronounced as when they're adults.
I got a good look at my fish today -- he's out and about more and seems less spooky already -- and he's definitely a dilectus. The red border on his fins wasn't so apparent at the LFS; his colour seems to have deepened overall, maybe he's more comfortable here. The red lines his dorsal and caudal fins, and there's absolutely no white on his face, no hint of a line at all. And no crazy huge teeth either, FWIW
I feel so relieved -- this LFS isn't always accurate in their labeling, and I had to take an (albeit very experienced) employee's word that this was indeed a dilectus. Glad to have it confirmed though -- it would be a disaster to release a terror into my reef when all I'm after is a tough little fish that won't take any crap from the angels, damsels or bossy yellow tang.