I think it was because we really don't know what exactly happened in the past. Also, I'm pretty sure people did not keep track of colored people back then.
As there were countless african people brought into slavery so we only have a rough estimate of the people.
We have only rough estimates of how many Africans were enslaved and brought to America due to a lack of systematic record-keeping, underestimations of populations, differences in cultural identities, high mortality rates during transport, and conflicts in Africa. These elements made accurate counting impossible, leading to only rough estimates by historians today.
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