Isn't this a key lesson in the study of history? There are no "definitive sources." Primary, Secondary, and Tertiary sources have their own biases, limitations, and cultural influences, sometimes to the point that they say more about their own lives than the history they portray. Sometimes it takes centuries for anyone to notice.

Your best hope for assembling an accurate picture of the past is to characterize how the biases you're aware of may have influenced the evidence available to you.