This variable is the unique number CMS assigns to each contract that a plan has with CMS. This was the Contract ID for the plan in 2017 (the reference year). It may or may not be the same as the Contract ID in the previous year (2016).
This field is a key that links of the plan sponsor's contract and plan identifiers.
All Contract and Plan ID that were active in 2017 appear in this data file. To determine whether the Contract and Plan IDs in the data file represent the same plan in the prior year, compare this variable (along with the corresponding PLAN_ID_17) to the CONTRACT_ID_16 (and PLAN_ID_16).
You need to know both the contract number and plan benefit package identification number (variable called PLAN_ID_YY) in order to identify the specific plan benefit package offered to beneficiaries for the particular year (YY).
This variable corresponds with the CONTRACT_NAME variable in the Plan Base File for the year, which is the contract name that corresponds with this number.
The CCW constructs the Plan Characteristics File from information submitted by plan sponsors to CMS’s Health Plan Management System (HPMS).
Source: CMS (HPMS Files)