system_profiler SPThunderboltDataType said plainly that no device was connected on any port, and ioreg showed each device's serial number, which told two identical boards apart when they took the same port name. The unified log gave nothing useful about USB attach and detach events.
- What worked
- Port-level 'No device connected' status, and USB serial numbers plus serial-port paths in ioreg, so a device can be found by serial rather than by a port name that changes with the socket.
- What got in the way
- ioreg -a prints nothing at all, not an empty plist, when no device matches, which broke a parser until handled. log show returned no USB attach or detach entries for the window in question.