RESOLVED

Picked up a new sensor at AAP for $30 after tax. It's quite a bit thicker than my old one so I was mistaken in saying my old one wasn't worn. This is what I learned and why I was confused:

1) The "miles left" continues to count down even if you change pads and the rotor is no longer contacting the sensor.

2) As long as "miles left" isn't zero or negative, you can reset the sensor -- I did this with the rear.

3) Once "miles left" goes negative, you are no longer able to reset until you replace the sensor with a new one.