I was reading Eusebius' work The Church History which says Tiberius "succeeded to the throne after the fifty-seven-year reign of Augustus". This appears to be inaccurate, being that this event mentioned occurred occurred in A.D. 14. 57 years before that was 44 B.C. yet Augustus became Emperor in 27 B.C., and 57 years from 27 B.C. is A.D. 31. Was Eusebius wrong or is there an explanation?
Most likely Eusebius was dating Augustus' reign from the time he was named Consul and recognized as the son of Julius, in 44 BC, or from the power-sharing agreement made with Marc Antony in 43 BC. The later date you give corresponds to his assuming the title "Augustus" and the formal leadership of the Senate. This may technically be how the reign of "Emperor Augustus" is dated, but Eusebius was apparently more interested in how long the man truly held the reins of Rome.