Is the Glass BSDF shader in Blender PBR accurate? So I was wondering whether or not the glass shader present within Blender is already PBR accurate. The only reason this sparks my attention is that I'm working on a watch at the moment in Blender, and I just want to ensure that the glass for the watch is PBR accurate. 

Any information about this would be greatly appreciated.
No, but you can get true PBR using the new Principled BSDF, which is available in the 2.79 RC 2 build.

To learn how to use the Principled BSDF I recommend watching this video by Blender Guru.