I was just checking out this Yosemite map from 1966 and couldn't help to notice all the designated "Trail Campsites" scattered throughout the backcountry of Yosemite. Pretty sure every single one of these designated trail campsites had at least one (if not more) campfire rings.
Also, on the map it shows "Tuolumne Meadows Lodge and High Sierra Camp" but DOES NOT show the Tuolumne Meadows Campground. So I wouldn't be surprised that all those old out-dated trail sign that lists "Tuolumne Meadows H.S.C." are actually referring to what is NOW KNOWN as the Tuolumne Meadows Campground.
This would explain the nice building (Tuolumne Meadows Reservation Office/Ski Hut) on the campground premises — a type of building not seen at any other Yosemite National Park campgrounds. They could have possibly been other canvas tent buildings (for the mess hall and showers) located where the campground is now situated. It would certainly explain some of layout of the current Tuolumne Meadows Campground. The current Tuolumne Meadows Grill and Store canvas building could have also been part of the old Tuolumne Meadows HSC.