Kieshi (+@doublevr) Thanks for confirming. After exercising it a bit I figured that was probably what was happening. That being said, I hope there are near term plans to expand that to the full library and remove the 100 limit (which really makes it not trustworthy since sometimes it doesn't display despite having watch progress). The utility in the progress bar on the thumbnail is a huge signal when rapidly browsing pages of scenes to know if you've encountered a scene before.
For example, if viewing a performer's scenes, and they have 10 pages of results -- the most efficient way today I've found to find what i haven't seen of theirs yet is to start from the first video on page 1 and go into it. Then have to wait for it to load. Then wait for the previous play position to get looked up. Then wait for it to seek to that position. Then it seeks to where it was left off (e.g. near the end of the video for one already watch). If the video is not new to me, can quickly click "next video" button in player ui and go to next and repeat until one loads that has no viewing progress (which can then be viewed then or added to a playlist). Since this requires loading all the video and scene data to begin playing to determine the previous watch status, it's very slow to go through pages of video. Then, if you end up actually doing that -- due to the "last 100" rule that is being applied to progress bar, all the progress bars move then to that one performer's scenes you just reviewed rapidly since they had many pages. Which then removes them from what you actually watched in full recently.
It'd be much nicer if the progress bar always showed the point in the video where playback would start if you restarted that video. That data is definitely available for more than the 100 videos since playback starts at the correct place. Just a matter of using it to show the progress bars instead of the other source of watch progress data with the 100 limit.
Hope the use-case helps.