Presumably the Vauxhall mentioned would provide exactly the measured MPG when driven at the correct speed by any owner in the real world - hence the 'flat spot' noticed.
The defeat concept you're referring to (presumably VW's) was set to only function during a test, and not in the real world (AIUI).
VW's defeat concept was set to function only at the exact RPM's used during the test. If a real-world customer were to use those RPM's and conditions, it would activate too. In fact a CCC talk showed that 5% of regular driving activated it.
Perhaps about 5% of regular vauxhall driving was in those flat spots...
Presumably the Vauxhall mentioned would provide exactly the measured MPG when driven at the correct speed by any owner in the real world - hence the 'flat spot' noticed.
The defeat concept you're referring to (presumably VW's) was set to only function during a test, and not in the real world (AIUI).