Bonjour Andrea
I am in no way whatsoever an expert on Greek aviation matters, but, please note that both Davilla and Sloan, in
French Aircraft of the First World War, and Gronxzewski and Fleischer, in Spad VII C.1, spell the unit term as follows: Mira. As well Davilla and Sloan state that the Spad VII in Greek service equipped the units 531 Mira and later 534 Mira. As stated I know little about the subject so, perhaps, DTB can offer you clarification.
Salut!
Kirk