It’s one of these things that probably did happen, but I would think Pershing and his descendants and maybe even the Army white washed the truth. It seemed that it is more than just a legend over there, it’s discussed as the truth.
We know for sure that his subordinates did this. Are there any examples of them being disciplined? No. I would think if you were in Pershing’s army, or Patton’s for that matter, you took your orders or your sense of orders, from their example.
If I’m betting, I’d say the story is probably true, or at least Pershing made these people back then think it was true.
The 49 killed story does not appear to have any solid references that have emerged so far, but focusing on those alleged details misses the real point of using pigs as a weapon against Muslim Terrorists.
There is a form of fallacy argument in which you attempt to dismiss the whole by finding one flaw in a minor detail. That is what is being attempted by the critics of Trump who say "The 49 killed thing never happened!"
They are attempting to deligitimize the entire point on the basis that some details might be not clearly supported by the record.
It's a form of lying.