The ripples in the pond following Ford’s disclosure that it never tested the 2013 C-Max Hybrid before affixing a 47 mpg sticker on it may go on for some time.

Since Ford downgraded the C-Max from “47 mpg” to “43 mpg” last week, it has also been learned that Ford justified the crossover hatchback hybrid’s 47 city / 47 highway / 47 combined figure based on what it arrived at after testing the Fusion Hybrid sedan under antiquated rules from the 1970s.

Ford’s Head of Global Product Development, Raj Nair, told reporters that these decades-old EPA rules allowed Ford to test the “highest volume variant” with the same powertrain as a basis for assigning a fuel economy figure on the C-Max. The rules predate the existence of hybrids which first entered the U.S. in 2000 in the form of the Toyota Prius which had launched in Japan a few years prior.

“So the Fusion is the highest volume variant in the family,” Nair said of its new hybrids that includes the C-Max.

Also true is the Fusion has been named in law suits as itself not meeting 47 mpg, although Ford did not discuss that in revealing details about the C-Max’s rating.

What’s more, the aerodynamic profile of the Fusion is different, and likely more efficient than the C-Max to which Ford assigned an identical mileage number by essentially following the letter of the law, but not paying attention to facts that would suggest the C-Max will return different results.

Whether the C-Max can reliably reach its estimated 43 mpg number may still be in question.

The fallout of allegations against both the C-Max and Fusion Hybrid has included a fair degree of online commentary. Some Internet readers have said they have one or the other of these two Ford hybrids and the “47 mpg” claims are easily attainable – and alternately, others have said the 47 mpg is impossible or very difficult to meet.

The new 43 mpg figure that Ford says the C-Max returns still exceeds what other reviewers said they have gotten, including those by Consumer Reports which said 39 mpg is more reasonable to expect of both the C-Max and Fusion Hybrid.

What Ford is saying regarding mileage expectations from its hybrids at this point is what many have already known. That is, hybrids are subject to a wider degree of variability in “real world” fuel economy.

For example, Automotive News noted a driver traveling at 75 mph might see a dip by as much as 7 mpg compared to the same car traveling 65 mph.

Or, in the case of weather-induced variances, a hybrid driven in 40 degrees F ambient temperatures may see a decline of 5 mpg compared to a balmy 70-degree day.

The Detroit News reports the C-Max was the only hybrid on the market which had not undergone its own fuel economy testing. Toyota in contrast has tested every individual hybrid it sells.

We shall see where this latest twist in the story goes.