Don't feel bad RBF, aint your fault, stuff just happens sometimes.. we went through similar.
None of our birds came down w/MS/MG symptoms, they had IBV, which is a non carrier virus. When I brought several for testing, the MS/MG antibodies showed up and I freaked, talked at length w/the avian vets and found out they had built up immunity, not that they were carriers.
Testing is a BIG help. I thought we'd had a Coryza outbreak and had already culled over 40 birds, when the second outbreak happened, thats when I tested and figured out what it really was (I felt so bad, I didn't have to cull the previous bunch which included several of my kids fav birds). They said there hadn't been a Coryza positive bird show up for at least 30yrs. Also, chickens CAN get colds, and they won't be carriers of it once they're well.
So, if you can convince DH to let you test, it'll save TONS of worrying and money (if you cull, you'll need to replace, right?).