“There is a possibility there were other elements to the deal. There might be something entirely secret that we don’t know and won’t know, something that it would be both in Russia’s and the US’s interests to keep behind closed doors. After all, that’s how the 1962 Cuban Missile Crisis was resolved, through quiet diplomacy, a complete picture of which wasn’t clear until later.”
https://www.vox.com/world/2022/12/8/23500092/brittney-griner-released-prisoner-swap-russia-us