It appears…that Ada scholars have overlooked the only Adelaida existing in major Russian literature. It is Adelaida Yepanchina, the middle daughter of General Yepanchin in Dostoevsky's The Idiot (1868). All three daughters have names starting with "A": Alexandra, Adelaida, Aglaya (compare this to Nabokov's Anya-Ada-Asya).
Fet, Victor and Slav N. Gratchev. “Another Adelaida: Dostoevsky’s The Idiot in Nabokov’s Ada.” The Nabokovian, no. 74, Spring/Fall, 2015, pp. 6-10.