This is the internal entry number of the Patient from
the PATIENT (#2) File.
This variable is optional. If passed in, the call
will return the enrollment category for this status rather than the veteran's
current enrollment status.
This represents the current enrollment category for
the patient or the enrollment category of the status passed in, if available.
Otherwise, it defaults to the "Not Enrolled" category. This will be one of
three values: "E" for Enrolled; "N" for Not Enrolled; "P" for In Process.