My recollection from a couple of your prior posts is that you have been using potato flour, not potato flakes. As it so happens, Bob's Red Mill sells both potato flakes and potato flour. The potato flakes are made from dehydrated Idaho Russet potatoes, which fits nicely with the original recipe, plus mono and diglycerides from vegetable oil, and citric acid. The potato flour is made from 100% dehydrated potatoes, but the particular variety of potatoes used is not mentioned on the label.
Most baked goods that use potatoes, such as breads, buns, rolls, donuts, etc., tend to use potato flour, so I think you should be able to substitute the potato flour you have been using for potato flakes. The quantity you would use, however, would be different. This shouldn't be a problem if you are using baker's percents/weights. Also, since both potato flour and potato flakes appear to have the same moisture content (about 6.5%), I don't think you will have to alter the formula hydration.
You may have already noticed that you can get dehydrated potato flakes in the supermarket. However, most such products usually include sodium bisulfite, which is added to prevent discoloration of the potatoes. The downside of the sodium bisulfite, according to Tom Lehmann, is that the bisulfite interferes with yeast activity if used in a dough product. So, I would tend to go with the unadulterated kind, whether it is the Bob"s Red Mill or some other comparable brand.