2mm wear between inspections then? There is an age element to this as well. Once they get to 6mm then it is very likely that what is visible hanging over the edge of the disc is 6mm but the rusty edge of the disc has cut into the lining and what is on the rest of the pad is lower or one pad is at 6 and the other is at 2 . Once the lining gets thinner so its ability to absorb heat decreases and the material deteriorates along with a certain amount of increased disc wear. If work is going to get busy soon then it is time to plan on having a proper look at everything to do with the brake wheel ends, pads are cheap, the discs and calipers aren’t. Get good quality pads in stock ready, you will need them even if that turns out to be not until next year.