British official histories could begin while a war was still being fought. The Second World War history is tentatively dated to 1940, with discussion of it beginning earlier. Gathering information contemporaneously was intended to support analysis and preparation for future operations or conflicts. Britain also formerly kept a list of historians with appropriate qualifications and security clearances for official work. Whether that list still existed at the time of the recording is left uncertain.
Notable Point · 35:48-37:03
Why official histories begin before a war is over
Contemporary evidence collection and qualified official historians allowed historical analysis to begin during wartime.