In China, there is a discrepancy between the "official" numbers and the actual numbers. For example, in monasteries, there may be an official number that is permitted by the government, and then a much larger number of monks who are actually resident in the monastery.  This dichotomy between "official" and "non-official" resident numbers can also exist in other contexts, such as for a city where ethnic distribution is distorted since a large number of ethnically Chinese residents may not be included in the official numbers since they are migrant laborers, or living off of the books.