The "I guess we'll never know how" situation doesn't apply here, because Samsung has just opened up about the measures it took to maintain the secrecy in the run up to the launch of the Galaxy S III. The project was so top secret that engineer Buyong-Joon Lee even denied what he was doing to his 11 year old son. Talk about commitment!
The lab also had high security, with handsets being moved between facilities in locked boxes and prototypes were personally delivered by a globetrotting executive to network partners. They went as far as to produce three entirely different models, each made as if it was the final product.
The lengths a corporation takes to hide even their biggest product from their internal staff.