LicoriceAllsorts
Donator
Since this is a headcanon question, here's what I think:
Aerith's communication with the Planet is patchy at best, and as she herself tells Cloud, she often doesn't understand what it's saying. In my headcanon, Tseng told her Zack was dead after the Nibelheim incident, because he was effectively dead, and believing he was dead would help her to move on. However, since Aerith thought she would feel Zack's passing, she was unable to believe he was dead, so she assumed Tseng was lying to her, most probably to protect her feelings. When she started writing the letters and Tseng started accepting them, her belief that Zack was alive was confirmed - which must have begged the question in her mind of why he never got in touch.
After Zack died for real, Tseng brought her letters back to her and told her Zack had been killed fighting a monster in the wasteland, because that was the cover story for the big battle surrounding his death that had given out by the Shinra News Network. Aerith, however, continued to refuse to believe Tseng, for a number of reasons. 1) most importantly, she didn't want Zack to be dead, 2) she no longer trusted Tseng, since he had patently lied to her before, and 3) the continued existence of Cloud, plus the fact that Sephiroth must have been stirring by this point, was blurring the already hard-to-decipher communications she was receiving from the Planet. She definitely felt something when Zack died, but she wasn't sure what it signified. The one thing she was sure about was that Shinra was in some way connected to whatever had befallen Zack. In Tseng's presence she burned her own letters to ensure they would never fall into Shinra's hands, and then told Tseng she was thinking of leaving Midgar, ostensibly to "find herself" but also to see if she could discover what had actually happened to Zack.
Kunsel had no time to say anything to Aerith about Zack escaping, because one of the Turks overheard him, in a bar, shooting his mouth off to some third classes about Zack (Kunsel never could resist showing off how much he knew), and that was the end of him.
That's my take on the subject.
Aerith's communication with the Planet is patchy at best, and as she herself tells Cloud, she often doesn't understand what it's saying. In my headcanon, Tseng told her Zack was dead after the Nibelheim incident, because he was effectively dead, and believing he was dead would help her to move on. However, since Aerith thought she would feel Zack's passing, she was unable to believe he was dead, so she assumed Tseng was lying to her, most probably to protect her feelings. When she started writing the letters and Tseng started accepting them, her belief that Zack was alive was confirmed - which must have begged the question in her mind of why he never got in touch.
After Zack died for real, Tseng brought her letters back to her and told her Zack had been killed fighting a monster in the wasteland, because that was the cover story for the big battle surrounding his death that had given out by the Shinra News Network. Aerith, however, continued to refuse to believe Tseng, for a number of reasons. 1) most importantly, she didn't want Zack to be dead, 2) she no longer trusted Tseng, since he had patently lied to her before, and 3) the continued existence of Cloud, plus the fact that Sephiroth must have been stirring by this point, was blurring the already hard-to-decipher communications she was receiving from the Planet. She definitely felt something when Zack died, but she wasn't sure what it signified. The one thing she was sure about was that Shinra was in some way connected to whatever had befallen Zack. In Tseng's presence she burned her own letters to ensure they would never fall into Shinra's hands, and then told Tseng she was thinking of leaving Midgar, ostensibly to "find herself" but also to see if she could discover what had actually happened to Zack.
Kunsel had no time to say anything to Aerith about Zack escaping, because one of the Turks overheard him, in a bar, shooting his mouth off to some third classes about Zack (Kunsel never could resist showing off how much he knew), and that was the end of him.
That's my take on the subject.