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The parts that failed the 20% test were simply allocated to the next preferred value. The sequence of preferred values is designed so that can just about always be true.
Carbon composition resistors still have legitimate uses where they can survive higher voltages and surge currents. Also sometimes for low inductance in RF circuits though surface mount parts are usually better still for strays. Otherwise carbon film, metal oxide and metal film are better is all respects. For fixing vintage kit, 1W and 2W film resistors are often a good idea. They are often a similar size to old half watt resistors and will withstand a higher voltage than smaller modern parts.
For higher voltage capability the Vishay VR37 and VR68 parts are excellent. Readily available in UK/Europe, don't know about IS/Canada.
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