Like most organization, you probably have new staff starting constantly, especially around the start of each session. You may have staff start near the end of a pay period, after you've already generated your timesheet. Maybe you have a new employee whose hours were not entered onto the schedules yet. You don't want to remove all the timesheets and "Generate" them again because some employees have already signed off on their timesheets.
There is an option in the Timesheet Listing page called "Add TS for Employees"
This option allows you to add timesheets to the period for staff that weren't in the system when the timesheets were generated for the period, or whose hours were added after.
When you select the option, the system scans the employees who work on the schedule types associated with your payroll group and gives you a dialogue box where you can select which employees need to have a timesheet added. Find the employee you are missing in the drop down box, select them, then click the green "+":
Once you've built up your list of staff who don't have timesheets yet, click the "Try to Add ..." button:
The system runs through the list trying to create a new timesheet for each employee.
When the process completes you'll get an alert and any new timesheets will appear with the status of "Created":
You may then process the new timesheet according to your workflow.
Note: This option can also be used if you delete a timesheet from a pay period by accident.