I'm glad that was caught.
Al's knowledge is partially protected given that it's from beyond the scope of Poseidon's reach. However, Alchemist is a resident within the world in which Poseidon does have some measure of absolute power.
He could potentially force the issue and try to remember what's been erased but we're not talking about a little mental editing. Reality itself was altered in a way that's deeper and more focused than any of Alchemist's spells could readily manage. Even a wizard's
Unname spell is less thorough than what Poseidon's decree forced upon the world.
TLDR; Alchemist could use pre-DC memories to fill in the blanks but it's a Bad Idea and he might eat enough VP damage to croak.