With no explanation, label text_A→text_B with either "DON'T KNOW", "NO" or "YES".
text_A: According to Schwarzenegger, his parents were very strict: "Back then in Austria it was a very different world [...] if we did something bad or we disobeyed our parents, the rod was not spared." He grew up in a Catholic family who attended Mass every Sunday. Gustav had a preference for his elder son, Meinhard, over Arnold. Other family members maintain that Arnold's accusations of favoritism were unfounded, but Arnold alone continued to claim that his Gustav showed a "strong and blatant" suspicion that he was not Arnold's biological father. Schwarzenegger has said that his father had "no patience for listening or understanding your problems". He had a good relationship with his mother, with whom he kept in touch until her death.
text_B: Is it reasonable to assume that some kind of hidden correspondence (such as love letters hidden in a box, etc.) could have come to light during Gustav Schwarzenegger's lifetime that could have explained (if not excused) his poor treatment of Arnold relative to Meinhard?
NO.