Re: Temporal Cold War and the rest of Trek history
Picard: Yes, I... I remember you. You were there all the time. But... that ship... and all the Borg on it were destroyed...
Borg Queen: You think in such three-dimensional terms.
This is probably the key magic handwave line. Any explanation we can come up with, would be too primitive compared to Borg concepts of space and time.
Dr. Howard, Dr. Fine, Dr. Howard: For duty and humanity! --Men in Black (1934)