Had yet to be

"A Nato official said the raid was “an issue for the Polish authorities”, adding that the centre had yet to be accredited by Nato."

Why is the verb phrase "had yet to be" in the simple past as the adverb "yet" marks the future in the participle clause "adding that the centre had yet to be accredited by Nato" in the above sentence?

Does "adding" is "a carrier" of the simple past tense meaning "A Nato official said... and a Nato official added" thus backshifting "the centre has yet to be accredited" into "the centre had yet to be accredited"?