Is report field Course Content Time Spent accurate? Also, how can I tell if a manual Completion?

Summary: I am trying to figure out why some users in a LearnCenter Report show as 'completed' course status, even though Course Content Time Spent shows 00:00. Could that be a browser issue? Most users who completed the course show some time in that field, but I have a couple users who show as completing the course but no time on the report with Course Content Time Spent. I am thinking it is either not an accurate field, or something else such as someone manually completed them. Unfortunately I am not sure how to audit if a manual completion was done