How does the Imp Assistant score Secret Tomes, and when does it trigger?

Question

Accepted Answer

At game end it scores the number printed on your Imp Assistant for each Secret Tome you have, including major secrets and cards that count as Secret Tomes (for example 4 tomes at 4 each is 16). Its remove-two-cards effect triggers only when you acquire a Tome, not when something later becomes one.

Clank!: Catacombs

How does the Imp Assistant score Secret Tomes, and when does it trigger?