Should an employee be able to enter time on a Redwood time card before their assignment start date?

Our payroll folks have noticed a couple employees are able to enter time on an assignment before the official assignment start date. And this apparently has started happening since we transitioned to the Redwood time card (end of July). For example, an employee has an existing assignment (123456) that started in May, and they have a new assignment (123456-2) that starts on 8/14. The employee was able to enter time on 8/12 and 8/13. Oddly, the system didn't throw an error upon entry (it usually throws an error for a valid value attribute), but thankfully it didn't pay it out.