Sure, absolutely. Or the number could be lower, if one organized the categories differently. Or much much much higher if one made it an axiom for the survey that all those individuals not in communion with Rome are, in fact, their own ultimate authority, which will be defined as a denomination, for the purpose of the survey, and the number approximates the number of individuals Christians not in communion with the Holy Father.
Hyperbolic hypothetical example of how defining categories might effect results.
Whatever the number really is, I have no idea. Whole bunch, likely. I wish someone would make a professional effort to tackle the question.
Incidentally, re: a service at a mortuary. When my parish was hit with a really bad fire, we met for Mass at a local funeral home, for several months. They had kneelers.
GKC