Yes, there is a very well defined EPA test cycle to determine the FE label of every car. There is also a modification factor to lower the rating to account for more real world driving since nobody drives as carefully as the test cycle. This is why it is easy to get a better number than published especially on the highway. The modifier is about 20%. So if a vehicle attains 20 MPG in the test then the published number is 16 MPG. The need for this modifier is especially true with the Ecoboost engines as a boosted engine seems to be more sensitive to aggressive driving practices than a non-boosted engine.
Anyway, there is no guess or debate over the label data as it is available for any vehicle here (including information on how the measured data is modified and why):