Does it really matter? If the car is as pristine as you say, and it checks out mechanically (use a pro), and the price is reasonable then buy it! Clean non-molested (read stock) Zs are becoming increasingly rare. Buy it if you like it. I would rate in importance:
1. No salvage titles. 2. Straight body no major crash damage; 2. Originality; No butchered panels or mechanicals. 3. Reasonable mechanical soundness.