No it hasnt been verified that Roys crew killed 200 but knowing what we know about them it wouldnt be impossible.

Off the top of my head, DeMeo crew murders that have been pretty much verfied as true.......

Vinny Govonara (guy who broke Nino's nose)
George Byrum (Florida electrician)
Eppolito's (father and son)
Frank Amato (Big Pauls stupid son in law)
car thief Anthony Quinn and his teenage girlfriend
Chris Rosenborg
Danny Grillo
Mickey Spillane (Jimmy Coonans rival)
Frederick Todaro (porn film boss)
Joe Brocchini (made guy in another family who punched Roy in a row over porn)
Andrei Katz (guy who bought a stolen motor off Chris Rosenborg)
The Vacuum cleaner salesman who Roy thought was a Cuban hitman

I just pulled those quickly from my mind.
Most have been verified by a 3rd party or at least have a degree of credibility.