Earliest entitlement date on this record.

If there are multiple periods of disability, take the first disability entitlement date. Otherwise, for old-age or survivor with a prior disability, use the prior disability entitlement. Finally, for disability entitlement with only one period of disability, or old-age or survivor with no disability, use current entitlement. 

Note that for a survivor with no prior disability, this returns a date of zero. This function should probably not be used in that case.

WorkerDataGeneral Methods