Every facility has a reference date, from which they are accountable for the completeness of the data for cases diagnosed in that year through the present. Since a facility may request to move their reference date forward, there are some instances where a case’s diagnosis year falls before the facility’s reference date. This item, REFERENCE_DATE_FLAG, is coded 0 in cases where this occurs. A 1 signifies cases where the diagnosis year is on or after the reference date year. Reports for cases whose diagnosis date is prior to the reference date cannot be changed or updated by the facility. For this reason, PUF researchers may choose to omit cases where the diagnosis date precedes the reference date, depending on the nature of the study. Note that, depending on diagnosis year and cancer site, excluding cases with diagnosis year preceding the reference year may omit greater than 40% of cases.