Over at Wizards, they are still excerpting parts of the Dungeons of Dread "S series" modules in anticipation of their reprinting. The latest snippet (yes you'll need a sub) is on the Lost Caverns of Tsojcanth and Lawrence Shick's foreward actually revealed an interesting tidbit that I personally didn't know:
"S4 The Lost Caverns of Tsojcanth marked the end of the S series—and rightly so, because despite being based on a gilded-hole dungeon originally designed for a tournament in 1976, its updated version really belonged more to the '80s campaign-setting school of design than to the wild-and-woolly '70s. S1 through S3 were standalone modules that could be easily dropped into any DM's campaign, but Tsojcanth is firmly based in Gary's World of Greyhawk. Indeed, there’s evidence that Gary considered Tsojcanth part of a longer Greyhawk campaign, placing the adventure between T1–T4 The Temple of Elemental Evil and WG4 The Forgotten Temple of Tharizdun. (By this reckoning, The Village of Hommlet, The Temple of Elemental Evil, and Tsojcanth are thus the "lost" WG1 through WG3 modules.) So, Tsojcanth was published in the S series because it got completed out of order, but was too good to delay."
It may have been obvious to others, but in retrospect, yeah Lost Caverns is so much more Greyhawk setting appropriate than the vague Tomb of Horrors or White Plume Mountain for instance. Way back when I never understood (or cared) how these S-series mods got lumped together and now reading this it's definitely wasn't because they formed a cohesive story like in the Slave Lord series or the Giants-Drow saga. Temple of Elemental Evil-Lost Caverns-Forgotten Temple does make alot more sense!