Neither NDI or GRAS is required.
Chromadex was busy selling Niagen for a long time before they published the first human study and filed for NDI and GRAS.
For Dr Brenner to now fault Dr Sinclair on NMN seems very dishonest to me.
Of course there are many sellers of NMN and it is difficult to weed out those that might be junk. Those that post test results from 3rd party labs are probably a safe bet.
For Dr Brenner to say any NMN is contaminated with caffeine, without any proof, is quite desperate. Surely Chromadex tests the NMN from bigger sellers and would post results if they found caffeine in any samples.