HP LIF floppy disks and bad sectors

Hi, I have been reading about LIF format floppies, in particular as used on the HP Series 80 and 200. I found this description: ftp://ftp.hpmuseum.org/lif/lifutil/lif_over.txt an overview on MoHPC: http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/articles.cgi?read=24 and the HPDir utility: http://www.hp9845.net/9845/projects/hpdir/index.html Can anyone explain please how bad sectors are marked as 'spare' under LIF? The LIF overview states: "LIFUTIL cannot recognize "spared tracks" on a LIF disk. To explain ... when you format a LIF disk, not all the tracks may be good; so the formatting process marks them as "bad" or "spared" and they are not used. LIFUTIL is incapable of distinguishing a spared track from any other; so it will suck in the spared track along with any other tracks in the file or directory, leading to corrupted files or catalog reads." What I can't find is a description of the bytes encoded on the disk to mark a track as spare. One possibility is this is dealt with by the HP disk controller firmware, and so hidden to the operating system, which sees a LIF directory as per the above descriptions, without seeing the spare tracks. I am trying to find some floppies with spare tracks and then analyse them on a PC, hopefully someone has been there already and can shed some light on the mechanism used. Regards, John