I believe you are right. Looking through several of the other series NVR's I can't find firmware supporting version four.
Not sure you will find a manual solely for GUI 4. The most recent (that I could find) user manual for the I series covering version four can be found here: Baseline User Manual 4.1.50
Yeah I believe that manual is the most up to date for the I series Nvr and other series. The manual is a bit over the top for most though.
Ideally I’m looking for a basic document explains the playback and file management options.
The best I can find is this GUI 3.0 document.
If I could find a similar document for the GUI 4.0 that would be great.