The main base for the British Army in Italy was set up in Arquata, just north of Genoa, in November 1917, a large skeleton APO S.101 came into use, known used from the 9th of November.
For some unknown reason a temporary APO L 1 came into use for 3 days only on 8th, 9th and 10th December 1917
On the 11th of December a distinctive double ring APO S. 101 came into use, this was replaced by a normal APO L.1 in June 1918.
Examples of the temporary datestamp are attached
Frank Schofield