I clearly remember the title card of the movie where in Kathai & Paadalagal were attributed to RaajaQuote:
Originally Posted by MumbaiRamki
this page supports it i believe
http://www.imdb.com/title/tt0155896/
Moreover sujatha in his series of articles coming in Kumdam or AV about his association with film field have not mentioned NT, and he says he lost faith in giving/writing stories for movies in early 80's itself, as he had no more guts to see his stories getting butchered, and he is happy with writing only the dialogues.