It's not my comment. It's data presented in the report. My comment is taken directly from the chart I cited. So if you want to quarrel with it, you need to quarrel with those who compiled the data, I suppose.

You first misread my comment, and now you're misreading the chart, apparently, so let me explain: the chart I cited shows the percentage of claimed improvement in fuel economy which was actually delivered in real-world driving.

This is precisely what my comment said.

Edit: I think your confusion might lie in the math that you think is being done, perhaps? The chart is showing the DIFFERENCE between two numbers. It's not based on just the claimed improvement. It's the actual improvement divided by the claim.

GM made a claim of improvement and their performance actually went down, so their number is around -38%. Daimler was the next-worst at around 16%.