Thanks for feedback. Regarding to your question. Can't you actually use the overwrite session feature ? There are a number of reasons why I didn't implement automatic tracking for sessions, because of performance when using the bookmarks as storage as well as because you are free to open as many sessions as possible and not decide for yourself what you want to save or not. I understand that this is a limitation compared to other sessions but this addon is mostly intended for on-demand saving and not really tracking every step. Implementing this feature is not really easy but if I find the time I might try to implement a special option to do so. But just so you know... if you close open tabs, for sure you can loose data from the old session because everything will be constantly replaced. I know for sure that for some users that would not be a good idea, so the only way I can possible implement this is through a special option, and not as default behaviour.
In the meantime... In your case though, if you select the old session and press the Overwrite session button it should behave just as you want? Or is it not ?