Maybe I misread something here. Akechi had guards at every entrance and Kaede sneaked past the guards to give Inoue the food which contained Ken's message. Nobunaga then recalled a few hundred soldiers back to the city and hid them in the kitchen and temple lodgings. All of this happened before the morning of the attack.
How did he get those few hundred soldiers past Akechi's gate guards without Akechi or Saito being notified of this? Even if they found out at the last minute just as they entered the city to attack, they would still have prepared some kind of counter measure for those few hundred recalled soldiers.