Yes, this is my reasoning, too!
I am not sure how your TA can come up with a December release from previous years' patterns. These are the release dates from the previous years:
Fall 2018 - May 11, 2017
Summer 2018 - February 21, 2017
Winter 2018 - October 25, 2016
Fall 2017 - May 24, 2016
Summer 2017 - April 12, 2016
Winter 2017 - October 6, 2015
Fall 2016 - May 18, 2015
Summer 2016 - March 24, 2015
Winter 2016 - October 28, 2014
Fall 2015 - May 19, 2014
Summer 2015 - March 25, 2014
Winter 2015 - November 12, 2013
No December releases at all, the latest release was for 2015 when it was in November 2013.
My bet is on an announcement on 10/21 and booking starting on 10/25.