The consular date given by the text is incorrect because the seventh consulship of Constantius was in 354 with Constantius Caesar. Mommsen and Seeck correct it: CONSTANTIO A. III ET CONSTANTE A. II, that is 26 February 342. Moreover, the prefect of Egypt in 356 was Sebastianus.
Mommsen incorrectly adopted the version of the name "Longinianus" instead of "Longinus", attested in one of the manuscripts. Longinus is known to be a prefect of Egypt between 341 and 343 from the festal letters of Athanasius of Alexandria. See Delamaire 2005: 142.