I don’t think they are being properly categorized at all.
Case in point: I have a couple stockpiles dedicated to only stone, or only clay, or wood, etc. as many of us do to help sort out the mass of incoming resources for basic material storage. I do this before I have my chests and other containers sorted out and in places that makes sense for workshops. Hearthlings are storing the buff potions in those specified stockpiles even though nothing but that one type of resource should be going there. I’m not sure why they would do that because in my mind, if an item is not categorized in any properly designated stockpile, it should just get left laying wherever and never put in a stockpile. That’s how I thought the system worked originally but now they’ve gone and put them somewhere in a chest and I have so many it’s hard to check them all to see which one it was because they aren’t supposed to be in there with those items. Naughty Hearthlings hiding the potions! 