On Counting Baptists
If religious group X is well known in a society, and people have general assumptions about what that group believes and how it worships, then it is likely that a congregation will choose to identify with that body rather than another. In my hypothetical case, then, it is quite likely that the US congregation would call itself Baptist, while the Brazilian one would choose the term Pentecostal or evangélico, while the African might identify either as evangelical or as an African independent church. Despite the individual names, though, virtually nothing would differ between the different groups…
If I am right in this observation, that has some implications for religious statistics. Above all, it suggests that we should not put too much weight on denominational labels, or of raw numbers. Sometimes those figures can be useful in tracing trends. Often, though, denominations are really flags of convenience, which say little about the practice of congregations.
Because of the history of British and Dutch colonialism the Protestant denominations associated with those countries spread, using their denominational labels. Baptists denominations, as an American phenomenon, did not have the advantage of colonialism. So when Baptist theology (e.g. polity and sacramentology) spread in practice, those churches used different labels.
This does not in and of itself alter the global church consensus on these issues, but it is probably fair to say within the Pentecostal and Evangelical umbrella in the Global South, there are more practicing Baptists than the denominational label indicates.