Hi Mike
The variables for the procedure and welder qualifications are dealt with independently, so theoretically there is no problem getting multiple welders to perform the welding on the procedure test plate. The problem will be that at the end, practically none of the welders may be qualified to perform production welding if their deposited thickness was not sufficient. If it is a very thick test plate, then you may be OK, because once the deposited thickness per welder (per process) goes over 1/2 inch, they can weld all thicknesses.
I hope I have interpreted correctly that you want to qualify a procedure test, and simultaneously qualify the welders?
Regards
Niekie