Yes you have missed that a valid header may appear by chance somewhere near the end of main zip data. Because your algorithm will prefer picking up headers tow

Yes you have missed that a valid header may appear by chance somewhere near the end of main zip data. Because your algorithm will prefer picking up headers toward the front, it might misinterpret a valid file, even one without a magic number in the comment; if the last 64k-(actual header+comment size) happens to contain an apparently valid header.