This variable is the unique plan benefit package (PBP) identifier for the beneficiary’s Part D plan of record for the year. CMS assigns an identifier to each PBP within a contract that a Part D plan sponsor has with CMS.
If the beneficiary was enrolled in more than one plan during the year, this is the plan benefit package identifier for the plan in which the beneficiary was enrolled at the end of the year.
For 2006-2012, this variable was always encrypted to comply with CMS privacy rules.
You need to know both the Part D contract number (PLAN_CNTRCT_REC_ID) and plan benefit package number in order to identify the specific plan in which a beneficiary was enrolled.