What is a Data Date (Status Date)?
The data date is the as-of point for all project status: everything to its left is actuals, everything to its right is forecast. Every schedule update, EV calculation, and status report is meaningless without one — "we're 60% complete" begs the question: as of when?
Discipline point: all status inputs must be collected against the same data date; mixing Monday's progress with Thursday's costs produces reports that are precisely, confidently wrong.
Worked example
The monthly update sets the data date to June 30. Site quantities, timesheets, and invoices are all cut to that midnight; the scheduler statuses every activity against it, and the EV run compares plan-to-date with earned-to-date on identical terms. When the owner asks why an invoice dated July 2 isn't in the numbers — the data date is the answer, and the reason the numbers can be trusted at all.