Hi Scott,
probably these KB will provide answer on your question, so you will need to schedule "Collect Delta Software Inventory" policy to managed endpoints with Inventory Agent installed.
--// Open advanced settings of "Collect Delta Software Inventory" policy and check only required settings to get task execution more faster.
After Delta Software Inventory execution uninstalled software resource is reported in Inv_AddRemoveProgram database table with two entries: InstallFlag 1 and InstallFlag 0
http://www.symantec.com/docs/TECH223257
Software removed from managed computer still shows in Inv_AddRemoveProgram table of the CMDB_Database
http://www.symantec.com/docs/TECH196492
Thanks,
IP.