What classified staff histories can preserve

How useful is a classified history written close to events if it includes secrets such as Ultra and remains closed for decades?

Very useful, because it preserves contemporary institutional knowledge and classified evidence even when public access comes much later.

A secret institutional history written soon after a campaign would remain useful even if sensitive information delayed publication. Its authors could capture contemporary knowledge, reasoning, and classified evidence before memories and records dispersed. A later release under a long closure rule would delay access but not erase the source's research importance.