How do you know this for sure? Do you have contacts with every diver and every person that catches and sends fish to hobbyists in the states?
There is a world of people who keep fish privately in the states beyond the reefcentral crew.
First of all, my knowledge of Pomacanthids goes well beyond the "reef central crew". I've studied, researched, and kept angels for over 20 years and have spoken at clubs and conferences from San Diego to Boston to Miami on the topic, including one where I address the masked angel's history in ichthyology and the hobby...
Secondly, Genicanthus personatus is not a fish that "every diver and every person that catches and sends fish" has access to. It is a Hawaiian endemic, and a very deep water and rare one at that. I've traveled to Hawaii at least once a year over the past 10 years and have dived every island and gotten to know divers, collectors, exporters, public aquarists, and ichthyologists there... While many fish are exported from there, they are shipped out by just a few dozen exporters, and while I only know a few, it is a tight community and word travels fast.
The numbers of Genicanthus personatus documented from the Main Hawaiian Islands are few... in fact the species was not even discovered until 1972, despite all of the divers in Hawaii even at that time... At the two locations where most all collection takes place, Oahu and the Kona Coast, this fish is rare even at depths down to 450 feet... there are a select few individuals with the capability (or guts) to collect that deep in Hawaii. In October of 2007, it had been over ten years since one of these fish was collected in the main Hawaiian Islands, when we caught this fish...
http://www.reefcentral.com/forums/showthread.php?t=1234494 In 2007 that was the only group commercially collecting with rebreathers in Hawaii...
While there are indeed a world of people that collect fish privately in the US, there are a very select few that collect very high dollar fish... some of those choose to keep their collections off the internet (I know a few), but one place they cannot keep secret from is the industry... everyone has sources for fish, and those sources when it comes down to it are a select few... especially for high dollar fish. In this country there are very few of these hard core collectors willing to pay over five grand for one fish... much less a pair... Also, the personatus in the above linked thread was offered for sale in the US by many outlets... the collector would have preferred it stayed in the US in fact... yet there were no takers, so it went to Japan...
So if even one personatus somehow slipped through this network of people to some unknown end hobbyist the chances would be slim... but a pair adds another dimension putting this well into the "beyond a reasonable doubt". In fact, when Jack Randall described this species in 1975 a male had never been even documented! Jack theorized that a male personatus may have striping like some of the other members of the genus he described... only after its publication were two males trawled at Nihoa, and he published a second description for the male, which has no stripes!

This is not like some other rare fish (like some hybrids), that could trickle in unknowingly and may be out there...
Copps