I'd say when two conditions are true:

1) you have an established pattern of behavior of ignoring safety concerns (Challenger, Columbia), and

2) people are alleging that you are doing the same thing now, with independent auditing from the OIG backing them up,

that's sufficient to shift the burden of proof back onto you.

Your attempt at a gotcha with the heatshield is just ridiculous: everyone already agrees the heatshield works in small-scale testing. That's the entire problem! It failed on the actual mission and NASA couldn't explain why, so instead they pivoted to trying to explain why the failures don't matter.

(EDIT: As an addendum, I'll also add that you don't even need to go back to Columbia to find an example of NASA lying about safety to protect reputations. Remember when they insisted for months that the Starliner mission was going just fine, and then eventually they said the astronauts weren't coming back on it, and then it landed and the final report was that there multiple failures leaving it on the knife edge of total catastrophe? And remember how that was less than two years ago? You're a maniac if you take the safety claims of this organization at face value)