Anybody except for VW would be in a position to make a move regarding other manufacturers, according to a document linked elsewhere from a German auto magazine there is plenty of reason to suspect that other manufacturers are engaging in similar practices but nobody to date has proof.
So, yes, it’s trivial to show that the EPA had the same amount of knowledge against others as they had against VW, because the original document already had that.
If you want an easy to digest article on the subject please read:
http://www.autoblog.com/2015/09/23/researcher-how-vw-got-cau...
And if you want less easy to digest material go read the actual study pdfs (they're linked in the wikipedia article on 'dieselgate' and are very interesting reading but it will take some time there are 100+ pages there).
So you are way off base with the claims in this comment.
Note that the WVU report does not state that evidence of a cheating device has been found. It was merely the catalyst (pun intended) in the whole affair causing the EPA to put a much bigger effort into the VW engine than they had up to that point and this is where the cheating device was uncovered.
One of the big concerns with TTP/TTIP is that they will expand the use and applicability of ISDS processes and this could impact things like environmental legislation.
Part of the concern about the use of ISDS is that the hearings are generally held in secret.
In this case I guess if it could be proven that the US government disadvantaged VW by applying fines to them whilst not prosecuting other companies who have done similar things, then if ISDS applies to this trade, it may be possible for VW to sue...