Obviously, since no penalty is involved here in the States, any farrier can claim to have any level of certification from any organization.
Certification is voluntary.
Licensing, whether mandated at the state or federal level, means some form of competency testing and provision for enforcement. Most of us will agree that licensing will not insure what is generally accepted as good farriery, any more than a driver's license insures good driving. On the other hand, assuming the implementation of a valid testing procedure and no nonsensical grandfathering in of possible incompetents, the possession of a license will insure that a farrier has demonstrated the ability to shoe a horse to a reasonable standard. Licensing will also give the horse-owning public added civil recourse for a farrier's negligence. I don't think the state cares one way or the other if Dobbin gets what he needs, I think the licensing of farriers has become inevitable because of the necessity of state legislatures to milk every financial cow in sight in order to subsidize a citizenry who finds it more lucrative to be on the dole than to engage in honest labor.