[Coco] OS-9 sector allocation bitmap AKA LSN 1

[Willi Kusche]

Hi!

    While working on programs to convert OS-9 disk images from Apple
II format to CoCo format and back I noticed that bit zero of the last
bitmap byte is apparently set in all disk images I examined.  I looked
at about a dozen CoCo disk images and two Apple II images and bit zero
of the last bitmap byte was set in all of them.  Can anyone enlighten
me as to why this is so?

Willi