I went back and "marked as watched" many older videos (by going to the end of the video) to keep track of what I had watched and what not.
Now, when I watch new videos, older ones show as not watched (the progress bar is at 0 on the videos view). It seems there is a hard limit on the number of videos that have their watched progress displayed properly.
From looking at the network calls when loading a page of videos, it seems like the call postrender has the saved times information, and 'data.VideoBundle.times' is always limited to 100 videos, which doesn't seem to be related to the ones currently on the page (essentially always limiting to only showing the watched progress for the latest 100 videos that I've watched). Is this limitation intended or is there a plan to get the watched progress just for the page I'm currently looking at?