Apple’s UDIF format writes a 512-byte trailer whose first four bytes are koly. It points to the block table and the checksum data, and it lives at the end of the file.
A DMG that will not mount almost always fails the trailer checksum. hdiutil names the failing block, which is the fastest diagnosis available.
Where this came from
Notes like this one come out of the file library rather than out of a release schedule. The pages linked above are the entries that were being worked on when the note was written, and those entries are rebuilt with each release of the toolset, so a note can go out of date in a way a format page does not.
When that happens the note stays where it is and gets a correction at the bottom rather than being rewritten, because the point of most of these notes is the order things were tried in. The editors who write them are the ones who maintain the catalogue.