Yep, file sizes alone leak sufficient information to be an issue, but it's a bit of a hypothetical because that's not what actually happened. Clearly, Mike shouldn't have allowed multiple files (or should have specified some kind of overhead for multiple files), and clearly there are other tricks Patrick could have used, but with these unfortunate rules and this submission nothing seems to require keeping file order intact.
It's a good point about needing to know which files are compressed. On a philosophical level, I'm not sure whether that means there actually should be a way to know which file(s) are the compressed data, or that the rules are simply broken...
What I'm trying to argue is that any justifiable objection Mike could have made would have failed.
Unjustifiable objections could have been made but screw those, because they would cause legitimate compression to fail.
Unjustifiable objections will pretty much always exist if the rules are written in English. That doesn't mean the rules are broken, it means you use judgement and follow the purpose of the rules.
Mike's fate was sealed when he allowed multiple files without an overhead penalty. He could have removed all the metadata possible, simply having the files exist as separate entities was enough to ruin him.
It's a good point about needing to know which files are compressed. On a philosophical level, I'm not sure whether that means there actually should be a way to know which file(s) are the compressed data, or that the rules are simply broken...