My guess ... they have enough actual test knowledge to be able to make the public claims (because there was enough new information that the aerodynamic tires/20 more miles of range didn't need to be announced). I'd also venture a guess that the actual design is being held until finalized for a variety of reasons - leave something else to show for the wow factor in the future, don't give away all the secrets sooner than necessary, use the public interest as part of supplier contract negotiation, etc.