From a quick skimming online, it sounds like there's a policy to embargo private correspondence until all involved haven't been around for at least 5 years. In

From a quick skimming online, it sounds like there's a policy to embargo private correspondence until all involved haven't been around for at least 5 years. In this case, it seems that Russell took a much younger woman as his third wife: [Patricia Russell, Countess Russell](https://en.wikipedia.org/wiki/Patricia_Russell,_Countess_Russell https://en.wikipedia.org/wiki/Patricia_Russell,_Countess_Rus...). Wikipedia lists her as passing in 2004, so presumably there was an embargo on their correspondence until 2009.