U&M
I am not discussing who is right or wrong, I just give my experience as a supplier/advisor for Part NCC operators and the two audits and the results.
As far as "operation" is concerned, one of the audited customer (pilot owner single pilot) has the operating part, ( company, address, secretary etc.) in Luxembourg, but the plane flies from France and is hangared there. After a meeting with both authorities, France was the one that had to approve the manuals and deliver the certificate.