engineers are know to know how to calculate an engine efficiency. this is not the 60's and they can have a pretty decent knowledge of an engine performance profile by their simulations and knowledge of previous iterations of the same engines.
if this really was an internal 'conspiracy' it should have run from the engine engineers of this engine iteration, the previous iteration, the software developers that touched near the code, all the testers testing that software code, all the qa that ran the endless benches run for the engine to qualify for robustness (a very tight and monitor environment [1]), whomever touched that data afterward etc etc.
[1] think like this, photi not actual wv center: http://assets.slate.wvu.edu/resources/1117/1304968590.jpg
The CEO created pressure with his ambition for VW to become the world's largest auto manufacturer; meanwhile the company had a culture and structure that would allow for shortcuts to be taken.