EDIT: This is a feature on Infuse-iOS but not tvOS.
Adding the “Mark as Unwatched” menu item to the long press of the “Watched” button in addition to “Mark as Watched” specifically on partially watched episodes would solve correcting the watch data in a situation where users get partway thru what they think is their latest episode and realizing they missed the last episode and have to go back.
This is a simple addition to make users’ libraries and watch data more accurate and manageable - it’s how Plex handles this.