My car is travelling back in time

[Jeunemaitre]

Various environmental changes can affect your emissions.  If your car is warmed up completely it can produce less emissions, the weather can change emissions readouts as well.

The other thing that can effect the emissions of a vehicle, aside from it travelling back in time, is the quality and type of additives in the fuel you're using at the time of the test. If you've switched fueling stations in the past two years, this may have something to do with the differences you observed in the reports. However, I think the time travel explanation is the most likely in this case.