The Austrian composer Arnold Schoenberg published four string quartets, distributed over his lifetime. These were the String Quartet No. 1 in D minor, Op. 7 (1905), String Quartet No. 2 in F sharp minor, Op. 10 (1908), String Quartet No. 3, Op. 30 (1927), and the String Quartet No. 4, Op. 37 (1936).
Arnold Schoenberg published four pieces of music in his lifetime.
From the context, we know that Arnold Schoenberg published four string quartets, but we don't know if he published any other pieces of music. I think that the system was unable to make this distinction.