For a cancer to be fourth stage it should have spread elsewhere other than primary site. As per the recent report there is no definitive evidence of disease elsewhere (like lungs). The lesion seen on right side is seen in both scans . But the lefts sided abnormality is not reported in current scan (probably wasn’t a major lesion)

This report suggests that there is a lesion in l ft buccal mucosa which is persistent, however the lesion mentioned near the flap in June report haven't been mentioned here and the comparision hasn't been done. It's better to consult the scan centre who reported the January scan and get it compared...