Daniel Berlin, an attorney with regs experience, on another thread on HN, said: no, you can pretty much just respond to NHTSA with straightforward answers and whatever documentation you have, then arrange a conference with them to figure out what additional documentation you'd need to generate to move forward with your plans.

I don't believe it's the case that Hotz needed to incur six figure legal bills to respond to NHTSA's initial order. He probably could have responded to NHTSA personally, without counsel, and game-theoretically not damaged his potential outcomes at all. He had the option to find out, and threw it away.