I don't think you could have provided a more accurate description of "fell through a gap in the regulatory framework".
Anyway, the gap is to be closed in the upcoming Treasure Act amendments so if something similar was tried in future those involved would be in trouble.
If the Law (suspended in England since 1st May 1707) is going to be changed does that mean England and Wales will revert to "popular sovereignty"? Wont that effect Liz, Charlie and William? Do they know of these proposed changes? Or will the Law simply be changed to cover Iron...? That is gonna mean an awful lot of of work for the PAS and a horde of new Liason officers... Cometh the hour, cometh The State!
I don't think anything "was tried" in regard to this helmet. I think English Law (suspended in England since 1st May 1707) (and there is no Welsh Law) was fully applied to its fullest extent. I don't think anyone "would be in trouble" in the future at all!