The "Current Completion date" field is populated by taking the latest value from either the Header Period of Performance End Date, Item Period of Performance End Date or Item Delivery Date on non-option line items. For example, if you have a contract with a Header level Period of Performance End Date set for April 30th and you have a non-option line item Period of Performance End Date set for April 15th, the "Current Completion Date" field will be April 30.

If you have a combination of line items and option line items, the "Current Completion Date" will still pull the latest value from the Header Period of Performance, Item Period of Performance or Item Delivery Date from only those items which are not options.  However, the "Ultimate Completion Date" value will always be set to the latest date of the 3 aforementioned fields, regardless of whether there are options line items or not.