This does not seem reasonable.
Personally, I think practically all potions would originally be labeled (in some way). A select few could be purposely mislabeled for a variety of reasons, but there should originally be a way to quickly identify a potion.
So, the stupid Gnoll would most likely have a labeled potion. There is no real reason to rip off the label before giving it to the Gnoll.
On the other hand, stuff happens. Some percentage of potions should lose their labels unless they are engraved (like on tin vials or some such).
Additionally, not all labels should be in the same language or even in a language at all. They could be color coded, or numeric, or in different shaped vials, or some other technique.
But, it just does not make much sense for anyone to craft potions and not distinguish them in some manner.