If the holes your describing are similar to the ones I have then I suspect they're "wireworm" trails which I believe are click beetle larva. basically the larva burrow into the taters to feed.

I cut the damaged portions out but the potatoes themselves should be safe to eat.

..and the black balls could be the wireworm frass. You may have set a record for keeping potatoes in-ground. They are normally harvested in late summer to mid-autumn, say Halloween. Leaving them in-ground longer leaves them susceptible to pests and deformities.

"Ridges in them"? Or did you mean ridges on them, or perhaps cracks or fissures in them?

I'm sure it was a record. We all sort of forgot about them and I was outside and thought it might be a good time to check on them.

Yes sorry I meant ridges on them. They are deep crevices
on the potato, seems like a deformation.

What exactly is wireworm frass? Thank you both for the answers.

Frass is the feces excreted by caterpillars, grubs, and other insect larva.

Potatoes require very even soil moisture, otherwise all sorts of odd growth patterns can happen in the tubers.

It feels like a lost cause at my garden....damn wireworms!! They have decimated everything i plant. Carrots, onions,garlic, corn, potatoes, daffodils.....i cant pick up a handfull of soil without finding them. Even the container plants will be infested by the end of the season. I have been reduced to pepper plants. Nothing is safe. Is there a way to sterilize soil???? Good luck to you all who see them in your garden.