We have noticed that we have many connections that are no longer valid and when we do an autodiscovery these old connections are not deleted.
There is no code in Spectrum to remove old connections during an autodiscovery, this includes pingables and SNMP models.
Release : Spectrum 10.x, Spectrum 20.x. Spectrum 21.x
CA Spectrum discovery will not remove old/stale connections unless the connection has been updated on an interface that had a previous connection. For example, if you have a connection on Fa0 <->Fa0 and you change it to Fa1<->Fa1, Spectrum will create the new connection on Fa1<->Fa1 and will leave the old Fa0<->Fa0 connection there (even if you use the Discover Connections During Scheduled Discovery option). If you updated the connection from Fa0<->Fa0 to Fa0<->Fa1, then Spectrum WILL destroy the connection and create the Fa0<->Fa1 connection. It will not leave the old Fa0<->Fa0 connection.
Additional KB articles here