Wow. I should have known better than to post a comment. Too many experts out there.
I spoke to United, Delta and American. All three have a 330 day window. Good luck flying to Paris on Southwest.
Yes, S&D are the drivers. There is far more demand for travel to/within Europe in August than there is in Feb or March. How do I know this? I priced flights from Mar out to June in August. Prices went up significantly over that time. Why? S&D.
As far as seat selection goes, yes you can get bumped for odd reasons. That is the exception. It if the seat you want is already taken by someone who booked before you then you are out of luck.
All I should have said was I found the train to be a great option between Paris and Bordeaux.