I actually have a theory now as to why a lot of these errors are missed by the animators. It is possible that the errors occurred while the films were being rendered. When you render a video on a editing software it is possible for errors, that weren't there when you were editing or animating, to appear after it's been rendered. This has happened to me a few times and with a direct to video budget it is possible that more errors could show up during the rendering process. I'm not sure if that makes sense but hopefully you understand what I mean.