I have seen collector extensions come off, but never saw the actual collector it's self come off,,if it was bolted properly with tabs etc.
If welding is not acceptable at the collector, why is welding OK at the flange area at the head?? Maybe NHRA should tell the header manufactures to tether them there too. I have bolt on header extensions on my TTI headers. I will put tapered loc nuts on them with loc-tite, lock washers and drill the bolt for a cotter pin. Suppose that will pass??