If a user has not opened or entered any time into the timesheet for a period, then they are not shown in the billing->timesheet tabs or in any reports for that period. The system knows that the user is assigned to a client/project so knows that they should enter a timesheet. This means for a large number of users, it very difficult to see who needs to chased to enter their timesheet and easy to miss someone. This is a fundamental feature of a time reporting system and needs to be rectified. I shouldn't have to raise a suggestion to get something fixed, but your support guy had no other options.