There are interfaces with status "Not Present" as below:
If this status refers to interfaces which existed earlier on the device but are now removed, then shouldn't this entry be deleted permanently from Spectrum's Interfaces view automatically?
Spectrum is just relating what we see in the MIB of the device agent. For the "notPresent" status we find references to this from vendor sites.
Cisco has it defined in its mib for ifOperStatus:
1 : up
2 : down
3 : testing
4 : unknown
5 : dormant
6 : notPresent
7 : lowerLayerDown
MIB IF-MIB ;
"The current operational state of the interface. The testing(3) state indicates that no operational packets can be passed. If ifAdminStatus is down(2) then ifOperStatus should be down(2). If ifAdminStatus is changed to up(1) then ifOperStatus should change to up(1) if the interface is ready to transmit and receive network traffic; it should change to dormant(5) if the interface is waiting for external actions (such as a serial line waiting for an incoming connection); it should remain in the down(2) state if and only if there is a fault that prevents it from going to the up(1) state; It should remain in the notPresent(6) state if the interface has missing (typically, hardware) components. The cause of this state is most likely the interface has missing (typically, hardware) components or some change performed at the device end."
So to resolve this, try to delete (destroy) and re-discover the model to remove the "notPresent" status if the MIB data has changed to reflect the current status of the interface.