It could also be that Nehemiah was counting time by what the Jews today call a civil year, which begins in the month of Tishri, corresponding to September / October.
نَحَمِیا این ماه را نیز جزو بیستمین سال سلطنت اَرْتَحْشَستا (‏ اردشیر )‏ بیان می‌کند .‏