Feri passes from teacher to student through small covens and houses with no central registry, and general surveys of American Paganism count Wiccans and Pagans as one combined category without separating this smaller initiatory current from the larger traditions around it.
What would resolve this A survey that asked self-identified witches or Pagans specifically which initiatory lineage, if any, they belong to would let a Feri-specific figure be drawn where only a combined estimate exists today.
OpenChas S. Clifton, Her Hidden Children: The Rise of Wicca and Paganism in America