Is the book "Al-Fath Ar-Rabbani" a commentary on the entire Musnad of Imam Ahmad, or on only part of it?

The book "Al-Fath Ar-Rabbani" arranged and explained Imam Ahmad ibn Hanbal's Musnad in 24 parts. Ahmad Abdur-Rahman Al-Banna authored it up to the twenty-second part. Then Muhammad Abd Al-Wahhab Buhairi completed the twenty-second part, and a committee completed the twenty-third and twenty-fourth parts.