Hazmat, dunno about your aquarium. But CMAS organized a behind the scenes tour of the Shedd Aquarium's reef exhibit. What looks like a 50G tank is a misnomer, and from the main area they have several tanks that look like htey have 50 tangs in a small tank.
But from behind, it is one gigantic lake, literally tens of thousands of gallons, probably more. The partitions don't go all the way up for one, so the fish can get around a bit, but more to the point the water flows all the way through the exhibit, so the water volume is much larger.
I am assuming you added your tangs at the same time, and as juveniles? If not, your success does boggle my mind, as several of your species are known as aggressive fish towards not only tangs but towards anything similarly shaped (angels, butterflies, etc). And I DO wonder long run about the fish being overly cramped for space. Tangs are powerful swimmers...
All that said, I entirely agree with what you say about experiences differing wildly. I didn't mean to say the inches per gallon was at all firm.