There is one more dechiya, pushing Rosh Hashana to the next day, if the molad of Tishri would be in the afternoon of the day that Rosh Hashana would have been designated. By any other Rosh Chodash we would make two days Rosh Chodash and count the next month from the second day but by Rosh Hashana we count Tishri from the first day.
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