In this case, it will still be two installations.
Norton Security installations are counted as per device. The repeated software installations (aka reinstallations) onto the same device are not counted as when adding new devices.
It is important to know that you have the full control over used seats from within your Norton Account. There, you can add and remove devices as needed. This means that if a reinstallation, for whatever reason, shows up as a new installation, you can still remove the “old” device and have the seat available for additional computer or mobile device.
For more information refer to our FAQ about Norton Management.