So, all dials with notch at 3, are redial
That’s tough as I haven’t seen all dials with a notch at three !
But basically it seems to hold true. When redialling the orientation of the dial needs to maintained so the metal needs marking as the original paint will all be washed off. Obviously not necessary when the dial has markers, but for a dial that’s just painted it needs to be done. It’s most common to have a notch cut at three, but I’ve seen notches at 12 too.