The spell as I understand it requires the target item to be either well known or clearly visualized. If you don't know even so much as the shape of the container for the potion, then it is neither well known nor clearly visualized.
Those parameters, a particular potion, particular types of potions, and potions by a particular maker, are in fact more complex of a request then just "potion"!
Its like asuming a kid cant find all the pennies in a jar of coins, but that he can find all the pennies minted in a specific state or during a specific year.
Your assumed limitations of the spell are actually making the spell do more!
Are you basing your interpretations on the spell as presented in the SRD, or in the Player's Handbook?
Because as I said, the players handbook has an expanded definition of the spells use, and mentions that more general search parameters can be used.