What does mediainfo mean when it says a video is truncated?

I have two ways of checking for damaged video files. The first is using mediainfo and runs instantly:

mediainfo "$1" | grep --color 'IsTruncated'

The second is manually going through the video frame by frame in ffmpeg (takes several minutes of intense processing):

ffmpeg -v error -i "$1" -f null -

I understand what IsTruncated means if a video has been moved or downloaded and is interrupted. The file is too small, and video will stop playing once it hits that spot. But occasionally the first script will tell me there is a video that is truncated, but it plays just fine and all the way to the end. And when run, the second script doesn't give any error message at all. What does IsTruncated mean if the video seems to be fine? Is it possible to find out how much or which parts seem to be missing?