This is the 15000th most frequent Korean word.
발견됐던
"Was discovered" or "had been discovered."
발견됐던 is used as an adjective describing the dog.
어제 공원에서 발견됐던 강아지가 주인과 다시 만났어요.
The dog that was found in the park yesterday reunited with its owner.
발견됐던 functions as a descriptor for the artworks.
그 그림은 오래된 창고에서 발견됐던 예술 작품 중 하나예요.
That painting is one of the artworks that were discovered in an old warehouse.
발견됐던 is employed to modify the noun data to indicate those that were found.