Even if some expert(s) here can tell you what to look for, what is acceptable or not, etc., based on your descriptions and pictures and magnet tests, what will you then do with that information? Fire your contractors? Or insist they redo the shell based on a website's "ruling," or your magnet? I was suggesting a building dept rep as a way of getting authoritative third-party eyes on site, to do a proper inspection. A person that would be looking out for your best interests, not the bottom line of the contractors. But there doesn't seem to be any Midland City or Dale County building/planning dept's (which I find incredible).
Are you ever going to feel comfortable with what either of your contractors do, or tell you? I think your research is prudent, here and/or elsewhere, but I think you're delaying the inevitable. You have to get an expert in there to first determine what needs to be done, or redone, and then approach the PB about how this is going to be resolved. I just don't see how constructive it is going to be siting anything you might learn on the internet, or discover yourself.
I'd start shopping for an onsite expert asap, if it were me, to see if that was a possibility, both in terms of logistics and cost... and then go from there.