I am a 312 owner and I got the feeling that Sony does not update these tab the only update I had from update center was when I bought the tab and going from 4.1 to 4.2 the 321 got more updates we never had the last minor update ..... I always update the Sony apps when I see them listed here or XperiaBlog ....... must be in Sony forget list !!!!!!!!!!!
Samsung Galaxy S2 i9100M 4.3.1 (CM10.2)
Sony Xperia Tablet Z SGP312U1B 4.2.2 Stock rooted