Oh man, that tester can only check signal coming through the cable, not the physical condition of the line. If the mice didn't chew all the way through yet, you can still get a good reading until the copper breaks completely. Make sure you're looking for chewed spots in the jacket and any little piles of insulation dust, not just relying on your equipment to catch it.

Almost inedible is a strong way to put it... was it truly that bad or just a bit over seasoned? Two tablespoons on eight pounds doesn't sound crazy to me. Maybe the salt just pooled in spots during the rest. Could just trim the very outer layer next time instead of tossing the whole method. Dry brines are pretty forgiving usually.

Family dinners always find the weirdest stuff to argue about.