I don't know why you keep refering to the FEMA study, it was an initial study that was later superceded by the more detailed NIST, NCST study.
From the NIST study:
As a result of the recovery efforts of the Structural Engineers Association of New York, Federal
Emergency Management Agency/American Society of Civil Engineers, and the National Institute of
Standards and Technology (NIST), NIST possesses 236 structural steel elements from the World Trade
Center (WTC) buildings. These pieces represent a small fraction of the enormous amount of steel
examined at the various recovery yards where the debris was sent as the WTC site was cleared. Elements
located in or near the impact zone and fire damaged regions were emphasized in the selection process.
These samples include full exterior column panels, core columns, portions of the floor truss members,
channels used to attach the floor trusses to the interior columns, and other smaller structural components
(e.g., bolts, diagonal bracing straps, aluminum façade, etc.). These structural components were used for
evaluation and/or testing relative to the fire and structural response of the WTC buildings.
I think you need to carefully read these reports, it may clear up some of your questions about "discarded" materials, etc.