Admin has very strict rules about what winds up being a separate set and what winds up being a parallel.
Sets that were only available in factory set format that parallel a release are listed as parallel sets. If they were also available in packs as well as the factory sets, or only in pack form, then they get listed as a separate release.
This is why the Fleer Glossy, Topps Tiffany, and Stadium Club Member's Choice sets are listed as parallels - they were only available directly from the manufacturer in factory sets, their sole method of distribution.
-- Dan --
Note: Please see my profile for more info regarding trading (section updated 3/4/2024). I have added a large portion of my inventory to the site, and currently have trading turned on (details are in my profile).