Here is a complete sheet of airmail labels from Ala Littoria. Sheet not listed in Mair's catalog as 20. It's onlisted as 10 and 18 labels per sheet.
Year: 1935, Gummed. Günter Mair's catalogue no: - ITA-B-15, perforated 10 ¾ , sheets of 10(2x5) or
18(2x9) or 20(2x10), dark violet-blue or dark grey-blue or dark blue or light ultramarine/white, 4****