Apparently a mechanic's tool purchase deductions can entered as a total amount, but what should be entered as the Date Purchased?

From what I've read here on AnswerXchange, it is apparently okay for a mechanic to enter a total amount for deducting tool purchases (as opposed to entering individual tools/receipts), but what should be entered as the "Date purchased or acquired" in TurboTax? It appears I could either use an arbitrary date or possibly leave it blank. Thanks in advance.