Here's the deal, and I actually know this because I WAS THERE.
(I love saying that on the internet). The folks at RAAC are good people, and it was an honest mistake. As soon as PvtPyle and I made them aware of the mistake, they took immediate action to correct it and find a good solution with the ATF. We went with them to the ATF Tech Branch agents that were at the show.
My personal theory, which is totally unconfirmed, is that the Russians measured these guns from the end to the end of the barrel extension, not the bolt face. When done that way they come in at 18+, with the choke they come in at 19. The ATF official method is from crown to bolt face. Since the Saiga bolt rides so far into the barrel extension, you can see how this would be misunderstood by the Russians. When measured that way they come in at about 17.2 with out the choke.
Now here's the thing. The shotguns that came in on this batch were originally supposed to be shipped to EAA. So there are probably EAA import guns that are the same way. So even if you have an old one, pull your choke, and measure the barrel with a dowel down the barrel.
And for clarification, Customs checks guns on export, ATF checks the imports. So these went through the ATF not Customs.