Was there ever a potion scroll in Sarrow Cave? Some people remember it, some don’t, but there certainly is not one there now.
To expand on this a little, I went through all the known scrolls on an alt to map scrolls to their respective unlocks. As far as I can tell, there’s no scroll that unlocks drink of ithecac or lvl 20 potions of boosting x1.
I went there early in the game and think there are only 2 quest items, but no recipe scroll. I think some might have confused it with the Sorceress’ Tunnel, there is one indeed.