Yes I think we did talk about this. Originally Tishri was month one:
Exodus 12:1-2
1 The LORD said to Moses and Aaron in Egypt, 2 This month is to be for you the first month, the first month of your year.
This tells us that God was making Aviv the first month of the religious year. Present day Jews believe Tishri, now month seven, was originally the first month of the actual year and this is also shown in the Bible:
Exodus 34:22
“Celebrate the Festival of Weeks [Shavuot/Pentecost] with the first fruits of the wheat harvest, and the Festival of Ingathering [Tabernacles] at the turn of the year.”