Talents, no. Talents represent that special ability and complement skills and define your character.
The +5% to the starting profile is a significant add in context of how skills grow in game through career advancement.
They are not cumulative in career advancement. Unfortunately, this is not called out in the rules very well.
Mentioned was Skill Mastery in comments above, this is a good example of how Talents are not "mastered," but inherent to the career first encountered or later found. Hardy is a birth Talent as is Night Vision. Hardy might be said you have or don't have and as you enter a new career that provides Hardy again, does it make you "more hardy"? I don't think so.
More context can be found in specifics: A Bone Picker may pick Hardy at character inception over Resistance to Disease and advance to Camp Follower. The choices for the Camp Follower are Hardy or Sauve. Having taking Hardy, Sauve is the only option. It also means that the character must take Sauve in Camp Follower to exit (100 XP).
More context is no Advanced Careers offer Hardy as an option.1
1 I did not cross-index all the advanced careers to be able to say that is the case for all talents gained in Basic careers are not offered again in Advanced Careers.
I'll stipulate the oversight in the rules is subject to abuse. My arguments against stacking might cite: Night Vision. Do you become better at Night Vision? No. I think that the unwritten expectation is that adds to starting characteristics to the profile are one (1) time only, as are bonuses to skill checks, e.g., Menacing. The bonuses do not stack.
I will also cite Strike-to-Stun, as early as 2008, where this question was asked as well: Two rules questions.
Because of the lack of clarity I would not be surprised to find others with a contrary opinion, but lack of definition should not be assumed as "wiggle room."