Deleted a project with TFSDeleteProject and later created it again with the same name. Work Items from the original incarnation of the project continued to show up in reports for the new incarnation of the project.
Eventually found that work items created for the original incarnation of the project were deleted from the TfsWorkItemTracking database but not from the TFSWarehouse database.

Work Items not deleted from warehouse when project deleted by TFSDeleteProject
kwards3
Found a fix in the Warehouse Troubleshooting Guide . This was an issue relating to project name collision in [TFSWarehouse].[dbo].[Team Project].
Per Jimmy Li, "When there's a project name collision, the reports will not be able to find the proper project by name."
Toni Greco