One possible datapoint to consider - Fuel
Does your area use
1. Seasonal gasoline?
I ask because the months of availability of winterized/oxygenaed gas will likely have an effect on those numbers (as will seasonal average temperatures and number of miles in winter temps vs. summer temps).
Also, if your area changed to E10 gas year round anytime AFTER 06, that would also have an appreciable effect on your numbers.
Personally I don't log the gas receipts, but do spot check mileage at every single fill-up and I notice trends seasonally and with fuel types (not only on the Baja, but on all our vehicles, it can be even more pronounced on motorcycles - ours typically gain or lose 10 mpg without or with E-10 respectively).
That said - with mixed driving conditions and E10 I've pretty much seen 22 mpg from day one. With more highway and/or non E-10 I've seen as high as 26 mpg.