Regardless as to how the enumerators were instructed to classify people racially, they classified the people 'through their own eyes'. This means that one shouldn't put too much faith in what the enumerator wrote, because it was based on their biases and judgments, rather than on what was actually the case. So, classifications could easily change from enumerator to enumerator and census to census. (and the fact that there is ONLY the human race is another discussion) For the purpose of deciphering census documents, we still 'buy into' this notion of race, so to understand what it is we are looking at we need to keep in mind that many of the enumerators really didn't understand those so-called racial classifications, and the majority of folks listed on any census are mis-classified. There were many more classifications for African Americans (and others) than just Mulatto.