However, even if you combine each mainline protestant denomination and count say all Methodists as one, one still sees nearly 30,000 discrete entities who proclaim to be christian but who have no connection to any other christian entity.
Individual interpretation of scripture is what allows for the use of the 30,000 number and distinguishes these protestants from your example of religious orders. Furthermore, these orders have no theoretical authority to make dogma and must answer to a higher earthly authority. Thus, 30,000 has legitimacy
It's not MY reasoning. It is the reasoning employed by the people who came up with the 33,000 denomination figure for Protestants.
OK, I’m searching through the IRS PUB 78 database, and am finding 1,352 Catholic groups in the USA alone:
I don’t understand how the IRS PUB 78 records even relate to our discussion here, to be honest.