It is possible that other distinct dialect groups were already in existence during this period. Good candidates are the hypothethical ancestor languages of Alanian/Scytho-Sarmatian subgroup of Scythian in the far northwest; and the hypothetical "Old Parthian" (the Old Iranian ancestor of Parthian) in the near northwest, where original *dw > *b (paralleling the development of *ćw).
What may have also been in use at the time?
other distinct dialect groups