IMO, that's a bench type inductor substitution box, not a standard. Inductance standards are usually wound on inert cores, not ferrite. They change very little over time and very little with applied voltage, unlike ferrite cores. For this, I'd just go with the manufacturer's spec of 5 and 10%, unless you want to go through a very involved characterization process. FWIW, I've had similar boxes and have never actually found a use for one because they were incapable of the currents needed or because they couldn't do their job on multiple inches of wire away from the circuit.