You could have predicted this.
Focus (the German news magazine) put up some investigative journalism and came to realize that as the refugees have developed social networks and their own information....they've all come to realize that the EU has given favorite status to the Syrians. Once you get to Greece.....Syrians get processed faster and allowed to proceed without any interference. Well...there are numerous efforts now by the non-Syrians (Pakistani, Afghanistan, Iraq, etc).....to pretend to be Syrian.
Focus didn't come out and say anything about fake Syrian passports, but my guess is that it's part of the routine as well.
How many? Unknown.
It doesn't take an idiot to see the time difference and favorite status at work. It'll mean more and more people show up in Europe and Germany.....claiming to be Syrian but they simply aren't Syrian.
A big deal? I'm not sure. If you had 200,000 people a year transit this 'path' to Germany who were claiming they were Syrian but they weren't.....it'd eventually get figured out and there'd be some type of consequence. If you lie on your immigration form, that's justifiable reason to deny you permanent status. You could even be kicked out of Germany if you lied on the refugee form.
If this works well enough.....the African folks might also get into the fake deal and start trying to claim they were Syrian. Eventually, down the line in three or four years.....Germany would wake up and realize they have ten million refugees or immigrates who are claiming Syrian status, and staying in Germany. There were only 22 million Syrians prior to the war, so the math and population number will eventually get figured out.
Just another odd problem that you'd never imagine.