That lunar months typically could not begin before the first crescent was sighted is, on closer inspection, one of ancient chronology's most overrated and persistent assumptions.
Egyptian lunar months clearly began before first-crescent visibility, even if it is not clear exactly how the beginning of the months were determined (on the Egyptian lunar calendar, see Depuydt 1997).
If not by first-crescent sighting, how was the beginning of lunar months marked?
All peoples using lunar calendars must sooner or later have realized that calendrical lunar months do not ever need to be shorter than twenty-nine full days or longer than thirty days.
Evidence for Lunar Months Beginning before First-Crescent Visibility
The question arises: how did lunar months begin in Jerusalem in the first century C.
The sources do not tell us how lunar months began in Jerusalem in the first century C.
as the consul date suggests, lunar months could indeed begin before first-crescent sighting in first century C.
Fotheringham (1908, 1911) was the first to note and the only one ever to defend the position that the lunar months of the double dates seem to begin a little before first-crescent visibility.
And that is typical of the lunar months of the double dates, as Fotheringham first noted.
These lunar months too begin typically a little earlier than expected.
Many Muslim scholars agree on moon-sighting as the only acceptable way for determining the beginning of the new lunar month
as they root the practice of moon-sighting, particularly for Ramadan, in the Quranic and Prophetic injunctions.