The British census asked employers to record their workforce numbers. The responses to this instruction provide a unique resource on firm size. While the responses were digitized and included in the Individual Census Microdata (I-CeM) deposit, their format limits their utility. A further data deposit, the British Business Census of Entrepreneurs (BBCE), overcomes I-CeM's deficiencies by infilling data gaps and parsing employer and workforce data into separate fields. This paper evaluates the coverage in I-CeM and BBCE data for this specific census question, and compares these with the published census analysis of the same data. The results prove the benefits of the BBCE data over I-CeM on the subject of firm size, and demonstrate the need for caution in using the published tables.