Thank you @UMD ! Yes that’s right, it persists on soft reset but we’ve also found it persists on power cycle too with a large enough input capacitor.
We use retained memory a lot because our devices need to work offline too and they are useful for resuming the previous state without having to connect online (we also use manual mode and system threads) there is a very good description written by @rickkas7 here: Retained Memory Tips
A caveat though if using system threading, you must remember to add waitUntil(WiFi.ready) after entering listening mode to prevent it ruining our plans to avoid the subsequent heap memory allocation!
Let me know if your tests work and if you see any possible drawbacks.