Rossi's were more common in Altavilla Irpina than in Paduli which was the commune that the family originated from. Lorenzo Rossi's father was Pasquale Russo born to Paolo Russo and Grazia Perlengieri in Paduli during the year 1863.
Paolo Russo and Grazia Perlengieri brought their family to Altavilla Irpina sometime in the early 1880's. Here we can see Lorenzo's 1897 Atti di Nati birth entry from Altavilla Irpina side by side next to his father Pasquale Russo's excerpt from the Paduli 1863 Atti di Nati birth registers.
As the notaries relied on birth registers for future marriage or other registrations - that spelling error carried forward to Lorenzo's marriage and naturally to his own children. Interestly only Lorenzo Rossi and one of his sister's Maria Rossi where registered with "Rossi", the rest of the siblings had the correct Russo surname registered at birth. Given Maria presumably got married and her descendants would carry her husband's surname - Our Family Branch would be the only one that now carries the Rossi surname.