We limit the study of a coin or series to a single third party grading service (TPG), and usually PCGS.  This eliminates many arguments about different grading standards.  Although PCGS does not recognize the DDR and DDO/DDR as major varieties they will certify them as minor varieties.  To help with this project we have been able to add additional wording to labels for double die reverse, and doubled obverse/reverse minor varieties when needed.