If the MAC and construction is solid, then wrong decompression is achievable, both theoretically, practically and by design, in many different ways except the o

If the MAC and construction is solid, then wrong decompression is achievable, both theoretically, practically and by design, in many different ways except the one you mention - the rare collision. There likely won't be enough computation, ever, to trigger an accidental collision, even if was a galactic bitcoin equivalent. I'd only be worried about deliberate collisions, if the construction isn't sufficiently hard.