If you want to find out the work-in-progress (WIP) on your projects as of a specific date in the past, you can run the WIP Reconciliation report. Under the Options tab on the Customize Report dialog, select the date range (Date From and Date To) for which you want to know the WIP and run the report. The required value is displayed under the Closing Billable WIP column. Check the Core Help for more on running reports.