Yes please. They're not defined in the builtin "Help -> User's Manual" either, but they're used in the manual's example outputs.
Even the NEWS file only describes {a} (automatic), {u} (unused), and {p} (purged), scattered around in the list. There's no mention at all of the {b} in your example. -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org