The original version of the 1Watter keyer did not have the "V" or Version option.
Included with all the original 1W20 kits S/N 1 to 200.
Works with all 1Watters

Version 0 started shipping with serial number greated than 200
added beacon mode
Verify by doing a CMD and sending "V" 
Works with all 1Watters

Version 1 was never distributed

Version 2
added straight key detection
Works with all 1Watters

Version 3
added speed pot
Works with all 1Watters
Works with all 1Watters that add a Speed Potentiometer

Version 4 is the current production version
added natural sidetone
Works with all 1Watters that add the Sidetone Mod Resistors