From Census.gov:
Census Bureau, which conducts more than 100 surveys for the federal government, is continuing to ask about citizenship on other forms, which have sparked plenty of confusion around the country.
Unlike the census, these surveys collect responses from only a sample of households, and their results produce anonymized citizenship data that the government has relied on for years to, for example, protect the voting rights of racial minorities.
So I think they use data from other surveys for apportionment, then why not use that same data to determine the number of REAL CITIZENS for apportionment, is what they are saying.
If that is accurate, how do you know if you get counted?