There apparently were four versions. Original and three revisions. A wildcard search at a couple online parts sources lists model numbers with engineering codes of 0, 1, 2, and 3.
The service manual is just outlining the syntax of the model number, illustrating that the last digit is the engineering change code, of which there may be one or more revisions through the machine's production. I doubt Whirlpool knew at the time the manual was produced how many revisions there would be. If you notice, the service manual shows the original u-joint/boot design, dual pressure switches, and two-piece pump.
Calypso changes of which I'm aware:
- U-joint boot/inner dome revision
- Elimination of separate flood pressure switch
- Integrated pump/motor
- Update on softener dispenser (added vertical notches to the slots around the center tower, although this wasn't specific to the Calypso).
- Update on bleach nozzle gasket
- Programming change reducing the end-of-cycle fluff routine from 30 seconds to 8 seconds
Tom mentioned that the rinse sequence was changed, but no specific details.
My GVW9959KL0 was manuf'd 5th week of 2001. It has all the original design.
My GVW9959KQ1 was manuf'd 41st week of 2001. It has the updated u-joint (even before I replaced it), softener dispenser, and one pressure switch.
Both have the longer fluff and two-piece pump.