Let's say I have a single file I want to encrypt with AES and I encrypt it twice (first encrypt the unencrypted file, then encrypt the encrypted file again). The first time I use password 'ABC', the second time I use 'DEF'. So in theory the attacker would have to decrypt it first by providing 'ABC' as password which would result in still encrypted garbage data - so they would provide 'DEF' and then they succeed. I wonder, though, if they may decrypt my file with only one password - perhaps there exists a password that is neither 'ABC' nor 'DEF' that successfully decrypts the file and they accidentally succeed with this password when bruteforcing.
In other words:
ABC -> DEF -> plain file
XYZ (exists or not?) -> plain file
Does the existence of 'XYZ' depends on the algorithm(s) used and will it always/never/sometimes exist?