Complex sentence: Mendes himself could not clearly distinguish between the two groups, and many he viewed as Orthodox were members of the USoA; the epithets "Conservative" and "Orthodox" remained interchangeable for decades to come.
Split into simpler sentences: Mendes himself could not clearly differentiate between the two groups, and many he viewed as Orthodox were members of the USoA. The epithets "Conservative" and "Orthodox" remained interchangeable for decades to come.