from another forum and a response to my inquiry

PS-84 was the original SOVIET designation for the licence-produced DC-3. "PS" reads "Passazhirskiy Samolet", or "Passenger aircraft". The numerical code "84" was taken from the factory chosen for the series production of the DC-3, or Zavod (Factory) No.84 in Khimki. Moscow (evacuated to Tashkent in October 1941). When the Soviet aircraft were renamed after their General Designers in 1942 the PS-84 could for obvious reasons not be given the name of an American designer, but instead the Chief Engineer of Zavod No.84 Lisunov got this (undeserved) honor. Thus the family tree goes: DC-3 -> PS-84 -> Li-2! In German id documents the bird was apparently called PS-84 throughout the war.