The video breaks it all down into confirmed and assumed kills, with assumed kills happening when Hawkeye fires an arrow, but we don’t see it land.
Considering Hawkeye has perfect aim, he probably hit something, but to avoid nitpicking, those kills are labeled as assumed.
Interestingly, the video also tracks the number of arrows Hawkeye uses and recovers.
Youtuber Matt Solazzo cataloged every single enemy Hawkeye killed on screen in both The Avengers and Avengers: Age of Ultron, which are the two movies that best showcase his skillset, since Hawkeye didn’t kill anyone in Captain America: Civil War.