You are absolutely right, of course. I'm restocking after losing all my birds...over 100 this fall...to MG. MG is not a required test for NPIP, although you can ask for it. Since it can be carried by wild birds and can pass through the egg, most people don't bother. But a carrier can easily slip past quarantine and infect your whole flock. When I was under state quarantine, I found that they don't even try to track it (just make you kill off your birds or try to test out...our chickens all had to be destroyed, but we saved the turkeys.) as they figure at least 50% of the birds in this state are carriers. Still, I'm going NPIP because I rather hope that if I limit to NPIP then I should increase my chances of getting birds from places that do some biosecurity, anyway. Maybe. Hopefully. We'll see.
I waited to be tested until we moved, and had my new pens built (thank you DH!!). In Florida it is free, someone comes out from the Dept. of Agriculture. They test for Pullorum-typhoid, AI, and Exotic Newcastle Disease. The blood tests are done right then and resulted, they send of the mouth swabs which takes about 2 weeks. You have to be tested yearly.