Comment by smileybarry

BitLocker recovery keys are essentially the key to an at-rest, local copy of the real key. (I.e., they need access to the encrypted drive to get the real encryption key)

When you use a recovery key at preboot, it decrypts that on-disk backup copy of the encryption key with your numerical recovery key, and uses the decrypted form as the actual disk encryption key. Thus, you can delete & regenerate a recovery key, or even create several different recovery keys.