Companies are not required to mark parts made by suppliers.
As to who believes what, or doesn't, not my problem. MECGAR never has made a secret of it...?. Parts do not have to be marked with country of origin. Do you see "Made in Brazil" on a Ford engine?
Every "article" (i.e. magazines sold separately from a gun) of foreign origin, or its "container" (i.e. a gun) must be marked with its country of origin.
United States Code, Title 19, Section 1304