When the 5 British Divisions arrived in Italy in November 1917, a General Headquarters was set up in,
Pavia (for 24 hours) then Mantua (4 days) then Padua (16 days). A temporary datestamp was issued but no identity slugs were available, the blank datestamp was used possibly for less than 4 weeks.
Because in was blank it tended to be ignored by collectors and dealers, but if on an Italian postcard dated November/ Early December 1917, there is a good chance it is from GHQ. A temporary GQ datestamp came into use on 9th December 1917.
Frank Schofield