Add metricCat:PreEnrollment, metricCat:PostEnrollment and metricCat:PostCompletion and use these along with any other category to indicate what stage the data covers. e.g.
<> qdata:metricType metricCat:PreEnrollment ,
metricCat:HighWageOccupation .
would be a measurement of the number of subjects employed in a high-wage occupation before enrolling.