Your wrong Nellie, its widely known maize in dog food offers little nutritional content, they simply cannot digets it due to their small digestive system. It may not kill them or have negative effects but it doesnt add anything. Dogs do not need carbs they need meat protein. They do not transfer carbs into energy like we do, they in fact have the opposite and process protein into energy. Potato is a carbohydrate that as a root is easier digested than a grain.
Id think it were more the Pork that would have had an effect on them rather than the potato - Though Burns are still manufacturing the Pork and Potato so it mustnt have had that many bad reports.

The way their body works is the important thing in this - there is a technical term for the transfer of foods into energy which I cant think of at the minute but theirs is from protein not carbs. That is why a BARF diet is so good - as its just meat with some veg to give vitamins. Its not a carb based diet

edit: you may have heard that the green eyes of potato are poionous - which they are - just like they are to humans..?