They didn't receive nothing.

Italy entered the war, aiming to claim Dalmatia, Tarantino and Trieste. When the war ended, they got Trentino, they got Trieste, they got Zara and some other parts of Dalmatia. Since Dalmatia had joined the state of Serbs, Croats and Slovenes in 1918, and was largely Croatian in it's ethnic makeup, the Allies couldn't really give the Italians everything they wanted there. However, the Allies did give Southern Tyrol to the Italians, and when the Italians annexed Fiume, few complained.

The 'marred victory' myth was nothing more than that; a myth. The Italians got almost everything they came for, and were on the winning side. Hard economic times followed, but it cannot really be said that the Italian victory was 'marred'.