Just found a fascinating series of articles in brittanica.com. It has TONS of info about calenders and calender reform such as -

"To remove the immense discrepancy between calendar date and equinox, it was decided that the year known in modern times as 46 BC should have two intercalations. The first was the customary intercalation of the Roman republican calendar due that year, the insertion of 23 days following February 23. The second intercalation, to bring the calendar in step with the equinoxes, was achieved by inserting two additional months between the end of November and the beginning of December. This insertion amounted to an addition of 67 days, making a year of no less than 445 days and causing the beginning of March, 45 BC in the Roman republican calendar, to fall on what is still called January 1 of the Julian calendar."

Doesn't realy answer my original question but does explain some discrepancies in when the equinoxes were and why new year seems to have moved a whole three months!

Still looking for the definitive answer

The truth is out there....

D the G