"must have"...
Anyhow, it all depends just what it is you tested and how you tested it. What does 'clipped both ends' mean? Were you analysing the raw file or working with a raw processor, if so which one? How did you set the black and white levels? And so on.
The figures I gave don't say what is usable, they just show the extent of information content. What you consider usable and how you use it is up to you.