I think the article is pretty clear actually. The C919 is lagging behind on certifications.This doesnt have much sence, since they were talking about introducing it to customers by year end, how could be that percentage of certifying is so low?
I asume it is related to something else, like replacing most of the foreign parts/systems and recertify them all again?
Unless it passes all the tests, then it clearly isn't allowed to be flown or AFAIK delivered to customers
From article:
China Eastern Airlines Corp Ltd said in August it expected to receive its first C919 by the end of the year, but that would require the model to be certified.
COMAC is years behind its initial certification schedule