Thought History vs. Version Control
Thought history in TheBrain is simply provided as a log for tracking recent edits and changes. It is not designed as a mechanism for restoring previous versions of your thoughts or thought notes.
However, if you backup your brain daily, this will provide a way of saving your content incrementally over time, in case you ever need to capture any previous versions of your content at a later date.
In addition, if you are syncing your brain with the web client (cloud version), my recommendation is to sync manually rather than automatically. This will allow you to revert to the web client in real time if you need to quickly capture any previous note content that may have been changed (or lost) with the recent edits in the desktop.