I posted this 3 weeks...

I posted this 3 weeks ago.
https://hotcopper.com.au/posts/41485683/single
These were all the announcements I could find. Hopefully, it goes some way to address your concerns.
Remember this has passed two independent rigorous technical due diligences, both of which had access to the detailed testing results.
If the test results did not show consistent 4N the DDs obviously would have failed very quickly.
'Scaling up from the lab to the plant is in my opinion very risky'
Correct, that is a very big risk and one that had a lot of work put in by SMS and the KfW due diligence. Mitigations to address this risk were one of the major reasons why the plant CAPEX increased so much.
Also, remember it is not just about the impurities that remain after the process completes but significantly external contaminants introduced during the industrial process.