“Demographer Mary Gautier of the center said counting Catholics is really more art than science because parish rolls may not be up to date. Many Catholics drift from parish to parish without formally changing their membership and often don’t report deaths in their families, the newspaper said.”
This isn’t really relevant to counting. I live in a small city where we have 2 primary parishes and there are 3-4 in the smaller outlying communities. We belong as members to St. Mary’s as my wife’s family helped to build that church after immigrating from Germany. However, we most often attend the church across the city as we like the hour and music at the Mass. We go back and forth and know each community fairly well. But for counting purposeds, going from parish to parish simply doesn’t matter. We are counted once in the official parish we are registered at.
You believe that you are being counted at St. Mary's because you are "registered" there, even though you do not attend there often. How do you know you are not also being counted by the church across the city, for being a body counted at occupying a pew, or possibly for leaving a personal check in the offering plate? How does your wife know she is no longer being counted by the church in Germany, for having been baptized as a child in that parish?