You're right Titanfall 1 was out before EA access but the fineprint of EA Access literally said it was excluded from the program for about a year until it was added to the vault at E3 2015, and so far is the only game to do this.
Titanfall is a unique situation, and they haven't announced anything regarding EA Access trial dates, whereas every other game by EA due out this year has dates officially revealed. Kind of telling IMO when Battlefield 1 even has the dates officially confirmed, but Titanfall not even though they release like a week apart.
Maybe someone from Respawn that reads NeoGaf can clear up whether they're apart of EA Access or not?