You can add LinkStatus parameter to find_system to look for only your own sub-systems and not the ones from libraries. find_system(gcs,'BlockType','SubSystem','LinkStatus','none')
. The same way you can also add 'Mask' with 'on' or 'off' values to filter based on whether the block has a mask on it.
Is "Sine" a sub-system from your own library? Sine wave block from Simulink library would not show up if you search for 'BlockType' of 'SubSystem'.