I think a reasonable bar is when a person passes out of living memory. Once it’s reasonably likely the last person who knew them is also dead, there’s no materi

I think a reasonable bar is when a person passes out of living memory. Once it’s reasonably likely the last person who knew them is also dead, there’s no material harm that can be done by revealing their correspondence and the benefit to historians would outweigh any potential hurts to living people’s memory of someone.