The church has no central membership roll and has been repeatedly divided by succession disputes since the 1980s, so published estimates of several million adherents across more than five thousand branches are given as a general "by the early 2000s" figure rather than tied to one dated count.
What would resolve this A dated count from the church's own worldwide administration, or a fielded survey in Nigeria and Benin asking about Celestial Church of Christ membership specifically, would anchor the estimate to an actual year.
OpenDavid B. Barrett, Schism and Renewal in Africa: An Analysis of Six Thousand Contemporary Religious Movements