More info about the name "September"
September is an English name, derived from the month's name 'September', itself derived from the Latin 'septem', which means 'seven'. September was the 7th month of the year till about 153 BC because the year started on 1st March till then. It was only after the beginning of the year was moved to 1st January that it became the 9th month. Hence the inconsistency.