The DRG Grouper Version (DRGVER) is assigned by the HCFA DRG grouper during HCUP processing. For discharges occurring before October 1, 1991, DRGVER contains the DRG "revision" number. For discharges after that date, DRGVER contains the DRG "version" number (which is one value higher than the revision number). This coding scheme is consistent with the labeling of the DRG reference material, including the DRG coding books. Thus, on September 30, 1991 the DRGVER = 7; but on October 1, 1991 the DRGVER = 9.

With Version 25 of the DRGs (effective October 2007), CMS revised the DRG scheme (up to 540 DRGs) into over 700 Medicare-severity DRGs (MS-DRGs). First, DRGs were consolidated into 335 base MS-DRGs. Of these, 106 were split into two subgroups, and 152 were split into three subgroups, to arrive at 745 total MS-DRGs. The subgroups were based on the presence of complications or comorbidities (CCs) or major CCs (MCCs).