Thank you for adding me to this interesting discussion, @Naiffer_Host.
IPEC position paper clearly explained MAH should take responsibility for risk assessment. Excipient manufacturers help with assessment but it is not an obligation for them. On the other hand, the IPEC and the Lhasa nitrite consortium held a collaborative meeting to solve this issue. I think now excipient manufacturers are more friendly than before.
Some excipient manufacturers such as IFF, DFE Pharma, and Asahi Kasei, provide low nitrite-grade excipients. To buy their products is another way.
And I want to add the recent discussion in the community. As far as I know, we do not have a magic bullet for this issue. Worst case estimation may be available but it is considered too conservative. MAH may test the amount of nitrite in their excipients by itself.