Greece 1923/1923 - Ordinary stamp of the Kingdom of Italy, 1 Lira - Sassone catalogo specializzato

Large fragment of a registered, prepaid envelope franked with an ordinary stamp of the Kingdom of Italy of 1 Lira (Michetti/Effigies of Vittorio Emanuele III series) cancel "CORFÙ", simple circle with a black datestamp.
During the occupation of the island (August–September 1923), the Italian administration overprinted the Italian stamps with the specific inscription; in this case the overprint is not found, but the clear round cancellation "CORFU' - POSTE ITALIANE" with date 19.9.23 (19 September 1923) confirms the rarity from a historical-postal point of view even on a stamp without a overprint.
The occupation, as is known, lasted only a short time (from 31 August to 27 September 1923), so the correspondence sent in this very limited time frame is certainly rare and valuable, also because the Italian post office established on the island remained operational for a few days (from 11 to 26 September 1923).
The Italian post office in Corfu opened on 11 September, but the overprinted stamps arrived and were distributed only starting 20 September (this letter is dated 19 September, one day before the introduction of the overprinted stamps).
In the first 9 days of opening, the office used the ordinary stamps of the Kingdom of Italy (from the series then in use, such as the "Michetti" or the "Leoni") without any overprint.
Letters sent in these very few days are absolute rarities!
Paper label for registered mail bearing the wording "R - CORFU' - POSTE ITALIANE".
Destination addressed to "All' Ill.mo Sig. Preside del R. Liceo-Ginnasio Galileo-Galilei".
Uncommon and valuable combination, for specialists.
Sassone Specialized Catalog; in any case a lot to be examined with care.
The photos constitute an integral part of the description."