The mint (and most other herbs) regrow every day, so had you picked EVERY single mint on the map? If not, you could have gone off and gotten some more. But I agree that if the game knows in advance you'll need an item that day, maybe logic check it out and prevent you using it.
Viewing post in Briley Witch Chronicles (C64) comments
had you picked EVERY single mint on the map?
Yes, all mint leaves.
maybe if the plants kept returning from time to time.
or better, every certain number of character steps. (possible problem with correct operation of the time clock in c64)
or an NPC item store
or get items in a winning fight
some simple and effective solution.