A GDX file is an input data file to be used with the vSPD model.
GDX files are created from the SPD inputs extracted from an SPD case file. The naming convention for final pricing GDX files is described here. What's available here is a single GDX file each final pricing SPD case file that is associated with final prices.
GDX files for final pricing are available from 2004 until 1 November 2022 when real-time pricing was introduced and ex post final pricing ceased to exist. The GDX files from 2004 until about July 2009 may be of dubious quality, as they were cobbled together from various data sources rather than the SPD final pricing case files.
Adding files to this folder stopped on 1 November 2022 with the advent of real-time pricing.