This variable shows the date when the beneficiary first met the criteria for the muscular dystrophy indicator. The variable will be blank for beneficiaries that have never had the condition.
The earliest possible date for anyone in the CCW is January 1, 1999. If the beneficiary became eligible for Medicare after that, the earliest possible date will be some time after his/her coverage start date (i.e., the COVSTART variable in the Beneficiary File).
Source: CCW (derived)