If you were "getting on" your motor harder yesterday, you would have had worse average gas milage yesterday than you have today. Therefore, if your mpg reading is higher today, you are going to have a higher dte.
My car has adjusted it self and gotten higher miles on the dte and then goes lower and then higher.
I did it last week where my car said it had 36 miles left on the dte and the gas light came on. I just drove really smoothly and then it jumped to 41 dte and the light went out. I really don't think that computer is a work of science so don't trust it to be so. Also, know that it will say you are out of gas and still have about 4 gallons in there.
Also, someone on here posted that they went down a big hill and reset thier mpg reading. They then put the car in neutral and got up to 85 mph coasting. The computer told him his car was getting 99.9 mpg! hehehehe....