SAM Discovery (Network Sonar Discovery)

Apologies if this has been answered before, I have searched but can't find anything definitive.

When I execute the Network Sonar Discovery manually I can export to xls.
I have also found the report "Device Poling Details report" and identified that I can query the "Discovered Nodes" table for a list of discovered nodes.

What I'm looking for is a report or table that provides details of the nodes that have been added and/or removed since the previous discovery.

I have run some tests (with nodes switched off) and have noted that missing nodes continue to be present in the "Device Poling Details report" but are missing from the "Discovered Nodes" table.

Is there an inbuilt report in SAM that I'm missing?  I am looking to reconcile the nodes discovered by the Network Sonar Discovery with the CMDB in Service Now.
Currently my thought is that we will need to schedule SQL queries against the Discovered Nodes table, store results and execute a query to ascertain the delta between them.
I would have thought there was a history table somewhere, but I can't find it.