[Coco] Oddball disk format question

[Robert Gault]

Does anyone know how it might be possible to create a track where the 
track ID number does not match the disk location, the sectors have 
values 247 & 248, and there is data on sector 248?

I have determined the following. The track can be created by stepping to 
the desired location (T35) and issuing a Write Track command with an 
incorrect track value. The Coco controller will accept a sector value of 
248 even though it is not "legal. A sector with a value of 247 = $F7 
(which is a reserved Western Digital command) can coincidentally be 
created if the track ID is 164 when a crc is requested in the "wrong" 
place. $F5, $F5, $F5, $FE, $A4, $F7 will create $A1, $A1, $A1, $FE, 
$A4(track) ,$42(side), $F7(sector) because the crc of $A1A1A1FEA4 is 
$42F7. It is not possible to place the desired data on sector 247 during 
a format because it contains values in the range $F5-$FE and I can't 
access the sector with a disk zap program because of the mismatch 
between disk and track IDs.

This track actually exists and I'm speculating that it was not created 
on a Coco but on a more advanced computer with a more powerful disk 
controller. Any thoughts from the audience?