Does anyone know how far in advance of a census 'publication' the information was collected? For instance, if my ancestor's age on a census is listed as 50 yrs.,does this mean he is 50 at the year of the census, or is he 50 at the year the information was collected?

Information was usually collected between March and June of the year stated on the census (1851/1852, 1861, 1871, 1881, 1891, and 1901) and the ages given were generally how old the individual was between March and June of said year or the age they would be on their next birthday