In the new UX, the previous timesheet regarding a resource hire date is available to be posted. Classic UX does not show it.
This issue has been observed in CA PPM 15.3.
The issue cannot be reproduced in CA PPM 15.4.1. An error is shown (as expected):
com.niku.union.odf.exception.ODFValidationException: TMA-0906: Resource xxx, xxx starts on XX/XX/XX. Creating a timesheet requires an existing, active, resource who is open for time entry and has a time track mode set.