1) It wasnt NASA, it was a company (that still exists) called general atomic.
2) The speed was only about 3-4%C.
3) the treaty was signed by the US government (Treaties can be unsigned though 8-))) )
The "starship" variant wasn't serious, it was an intelectual exercise pushing the boundries of the technology. (the launch mass was arround 240 million tons and it would have to be built in orbit)
I dont know what sort of detail the programme will go into, "Practical" designs would cover launch weights rangeing from several thousand tons up to possibly several hundred thousand or even millions of tons!(I said they were huge)Unlike rockets, the drive system actually gets better the bigger you go!