When I was first on, there a button that checked off every episode to that point, I really liked that feature, is it still here, or does it need to be re added? If so, I suggest that, or a "Watched All" button, so I can just uncheck the ones I didn't watch.
This feature to mark all episodes you've watched before of a certain series is already here and can be found via your watching.
Watchlist -> (Your show) -> Click View All and it should be there.
Oh, I see. I knew I saw it somewhere before. Thanks!