When drilling into the value of billable time incurred in a period via any of the WIP reports you may find that the time subtotal does not always match the time subtotal in the Team and Individual performance reports.
This is caused by future-dated billable time entries featuring on invoices with an earlier invoice date. In order for the WIP to reconcile on the invoice date we must recognised the billable value of time incurred on the invoice date even though the time was incurred after the invoice date.
The Team and Individual performance reports provided the most reliable source of staff-time and staff-billable value information. When we're talking WIP however, use the WIP reports.