About "undo" memory in Dorico

I was wondering if the undo memory is kept in the saved project or instead it is just in the Dorico memory until it is closed as an application, or even on disk but privately.
So I can delete parts of my music in one project, save it with different name and attach a reduced project to one post of mine without having my music still in the new project.
I asked this because I created such a reduced project and saved with different name but I think it had my old music because it is still huge (3Mb instead of 4Mb).
In fact I see that undo is not available now after closing and reopening the project and the application. But before I am sure that another similar check failed without closing the application, so I kept undoing and the old music re-appeared.
What is the official stance on this?
Regards

Undo state is only preserved within the session. The undo history is cleared when you close the project.