If you signed up with an email code and later click Continue with Google (or the other way round), you'll see a message that an account with this email already exists — along with the method it uses. Go back and sign in with that method; your memories are there.
The same happens in the sign-in window your AI app opens when you connect it: it says which method the address is registered with and offers to sign you in that way.
Nothing is merged automatically, and no second account is created: JustOnce refuses the sign-in rather than splitting your vault across two identities.
Want to switch methods permanently — say, from email codes to Google? Contact [email protected] from the account's address and we'll rebind it for you.