وَهَذَا مُشْكِلٌ
This presents a difficulty.
Later ʿAbbāsid and other rulers were historically styled “caliphs.” How, then, can the statement about thirty years be understood? The objection exposes a difference between a broadly used title and a narrower religious-political ideal.
The reply distinguishes a political office called the caliphate from the specific caliphate modeled on early prophetic succession. Treating the two as interchangeable generates the apparent contradiction.