don't mean to hijack your post, but i have the same issue with our cabinets on a 58 house.
it was redone with new cabinets years ago.
maybe 20% of the drawers/doors are in need of refinishing
they are the particle(boise) board bodies, with the face frame and raised panel doors of solid oak.
they used a darker stain on them, and over the years the heavily used ones are showing a tremendous amount of wear.
also, we swapped out the handles, and some of the doors/drawers have black profiles of the old handles showing in the wood.
It seems this black staining occurs under the sink area, where moisture contact is likely the culprit. I don't believe it is mold.
Is there a chemical that will remove these black stains?
i don't mind stripping sanding and refinishing, but if only 20% of the drawer/door faces are in need of refinishing, i am concerned about the new finish not matching.