The UDT unused ports report shows "Never" for ports connected to other switches.
For example, Switch A Port aa -> Switch B port bb. The UDT unused port report shows "Days Since Last Used" as "Never" for these ports.
All UDT versions
UDT uses the presence of an Endpoint MAC address to determine if a port is Used.
This is by design. Also, it is verified that there is no MAC detected on the device using the "Show MAC Address-Table" command on the switch.