This variable is the Medicare Part C contract number for the beneficiary’s Medicare Advantage (MA) plan for a given month (May).
CMS assigns an identifier to each contract that a managed care plan has with CMS.
If the beneficiary was not enrolled in a managed care plan for a given month, this variable will be null/missing for that month.
You need to know both the Part C contract number (PTC_CNTRCT_ID_XX) and plan benefit package (PBP) in order to identify the specific plan in which a beneficiary was enrolled.
There are 12 monthly variables - where the 01 through 12 at the end of the variable name correspond with the month (e.g., 01 is January and 12 is December).
Source: CMS Common Medicare Environment (CME)