What is the ruling on repeating the verses or surahs recited in the first two rak‘ahs in the subsequent rak‘ahs?

Since in four-rak‘ah sunnah prayers each two rak‘ahs are considered independent (Ibn Abidin, Radd al-Muhtar, 2/16-17), reciting the same additional surahs in the third and fourth rak‘ahs as in the first and second does not harm the prayer. However, it is preferable for those who know other verses or surahs to recite different ones.

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu