Is USG Sheetrock(r) "SW Edge" a thing, or a feature?
The "SW edge" panels are a subtype of tapered edge panel. The USG panel products list link refers to a product performance brochure concerned only with the fire, mold, moisture, sag, abuse, impact, and shear resistance regarding the entire panel.

USG offers panels with a square edge only as a base panel, which is usually intended to be covered in its entirety with gypsum/plaster and sanded to a finish, or another layer of gypsum board.

USG also offers panels with tapered edges, in both the "conventional" and "SW edge." If you intend to meet the USG spec, this means it is necessary to pre-fill the "SW edge" taper with Durabond/EasySand.