All 'saved' Basket Titles and Registers are held 'locally' in the browser's cache you are using, not in Nimbus® itself. If you log out and back in using the same browser and computer, those documents should be 'saved' in your Basket - as long as the cache has not been cleared. In theory, they can be held indefinitely.
If you change either browser or computer/phone to go back into Nimbus®, those previous session's documents will not be held in the Basket. Can they be retrieved? Sadly, no.
A more permanent solution is to use the Save Favourites option at the bottom of the Information Panel. We have a Help Video about this you can watch HERE
I hope this is clear - if not, please reply with your question to this message.