EPA rating differences between years for same car?

[Daox]

I've noticed this a few times now. If you look up the same car on the EPA's website, it is possible it has different ratings from year to year. I'm aware manufacturers make small changes here and there, but enough to make an almost 10% difference in fuel economy? I just looked up the Civic HX and this is what the comparison showed. I'm not familiar with what changes were made to the HX over these years, but its all the same body style.

[TomO]

Actually the 99-00 Civics got a refreshed front fascia and changed the design. Emissions regulations could've played a role in the mileage decrease as well. I know there were a few different Code versions for the ECUs available for the different years. Also, did you compare all the CVT models or Manual models and not mix the two? The CVT models did not have a wideband O2 in them.

[Daox]

These are all manual trans.

[wagonman76]

I believe that for the 97 model year, carmakers had to have some sort of side impact door beams which changed the overall construction quite a bit. Maybe there were other changes needed too. GM chose to ditch the models that had been out awhile and would have needed major retooling.

[taco]

my 07 camry was rated at 33mpg highway in 08 when they estimated them it went to 30, but the 08-09 which are identical are 31mpg.

weird.

[PaleMelanesian]

According to this list, very little changed. Most of the changes were cosmetic for the 99 model.
6G Civic Trim Differences - Honda-Tech

[Daox]

Yeah, here is another example. They did make a change to a returnless fuel system in 97, but I'm pretty sure no changes were made in 98. However, this isn't as large of a difference, but still 2mpg on the highway from 97 to 98. It just doesn't make sense. Can there really be that much inconsistency in the EPA testing?