In Nethack, I find myself a ruby potion, and drinking it gives me poison. Later in the same dungeon, I find a "Liquor Emporium" (potion shop) and find other ruby potions in there as well. Do all items within the same dungeon have a constant effect (e.g. All ruby potions are poisonous)?
Item effects for similar descriptions will inherited within an ascension run, but are randomized at the start of a run. Taking your ruby potion for example. If you drink one and it poisons you then all ruby potions are poisonous for that run. If you die or ascend and start a new run, then the effects of a ruby potion will be randomized at the start of that run. It may be poison or may be something else.