But I think I may go back and decide what they prepped, and then see how to collides with reality.
Mind you, in one story, they have a clue what they face (but not two clues, and certainly not three), and in the other, they are blind-sided, but in both cases, they hit a critical point when they are low on spells -- for one they have to rest, for the other, they are attacked by a traitor, and this way I can plausibly have them blow some spell slots on spells they can't use.
Such is life with high-level spellcasters in Gamelit.