This variable provides the application number (k = 1 to 4) that matches with the date of filing for benefits. This variable pertains to mbr_ssdi_ben_dof. The MBR has information, when applicable, on the date of filing of the most recent accepted OASDI application and the date of filing for most recent rejected OASDI application. If an individual's SSDI history and one of their SSDI applications in the SSB aligns with the timing of the date of filing for the most recent accepted application, mbr_ssdi_bdof_app will indicate which application number k.