You would have discussed on New Year subject more. One more i stumbled recently.
Looks in vedic times New year started somewhere near Margazhi full moon.
In "Muthee Ombal" Agrahayani is an importatnt sacrifice. Hence it looks that the New year started some where around this time. Hence the Thai New year logic has some support.
On the Margazhi full moon, apart from completing the sarpabali, the pakayajna called "agrahayani" must be performed. Like "sravani", the name "agrahayani" is also derived from the name of the month of the same name - Agrahayani is Margazhi. "Hayana" means "year" and the first month of the year is "Agrahayana". In ancient times the year started with this month. The first of January [of the Gregorian calendar] falls in mid-Margazhi.