Per NFPA 80, only one layer of drywall is required to be within the frame.
We contacted the testing and certification company UL to provide more information and help clear this up.
For walls with fire durations greater than one hour where multiple layers of drywall are attached to the studs; the additional layers of drywall can be hung so that the additional layer(s) is (are) butted up directly against the frame return.
This method of installation is specific to those frames provided with steel or wood stud type drywall anchors. It is UL’s experience that the single layer inserted into the frame on each side of the stud is sufficient to maintain the hourly rating of the door opening.