Life is too short to be pissed about fairly minor things that occured in the past. That said, if you ever bring the car back to them, explain to them that they have driven the car in the past when you have directly told them not to. Now, you want to walk out to the car with the service guy and agree on the odometer value prior to leaving. The explicit agreement is that that odometer value will be the same when you pick the car up, plus a few tenths.
Or you could just use Mitch since you're out of warranty now.
Or you could just use Mitch since you're out of warranty now.