I think the only fair grading system, would be;
knowledge
ability
experience
possibly, with an associate membership for non working, bit involved in the business, personnel.
As I said many times..............the basic / entry level could be, by completion of a pretty basic questionaire, avoiding resistance from older participants, who might feer embarassment.
Further gradings, could still be done through distance learning with practical elements taken, in groups, by independent supervisor.