Here's my take, as a Detroit native and working in the auto industry all my life.
This is ....probably...the work of an overzealous group within VW that did some performance enchantment to the tune to please some testers/magazine review etc. If you don't think they all do this, think again. They do. From the info I know, the "bad" mode (or good mode was most of us would call it) is only triggered by going over 85mph once. This is sketchy preliminary info, so..take it for what it is, but nevertheless, I wouldn't say without some first hand knowledge.
A guy that works for me has a 2015 Golf with this suspect engine. 2.0 TDI. He has about 5kmi on this car. I told him, go 90 for a spell, then see after a few days how the car is performing. He reported, gas mileage went up from solid 38-42 range to 46-49 range. He reported a much more responsive turbo and just general all around better performance.
So...taking all that into account, I would surmise, the vast majority of the vehicles in question, are still compliant. The "detect" mode is going over 85mph, once. That was, ... probably..... to please some specific maganize or review test, and they somehow lost sight of the emissions in that mode.
But...it's all moot, the media is already in kill mode with a "defeat device" and "admitting" and "harmful to your health" narrative. Yeah, harmful to your health, as in every diesel prior to 2007. We're all just keeling over here for NOx emissions.
VW is admitting a couple cars presented to them seems to not meet emissions to standards as they were tested. They're admitting they don't know why. The media wants to say they knew, they did it un-purpose, without evidence. However, knowing all all OEM's sometimes doctor their tunes to meet a certain condition...this is my guess. A group tuned it to perform for some condition, and didn't take emissions output into account during that condition. And as far as I know, the condition, is, go over 85mph, then the car is in "performance mode" forever more. So...my guess...most cars have not gone over 85 and are therefor compliant, but VW is already lambasted in the media, and will have a tough go at explaining that.
Rest assured, we're all losers in this. As the EU and US will most undoubtedly make regulations for diesels even more stringent.