Direct at the end of the audit: "I have checked every serial number." Years after the audit had been closed, its findings superseded and all the audited equipment scrapped, Ravi said he ___.

Explanation

Had checked backshifts the completed statement inside a long-closed frame: the audit ended years ago, its findings were superseded and the equipment was scrapped. Have checked breaks subject-verb agreement after he, was checking wrongly presents the finished audit as an ongoing background, and would check turns a completed act into a future-in-the-past.