Include the Original Corpus Specification in the documentation. It might contain important information for the user that you are not aware of. Also, it might be useful for colleagues that plan to work on similar speech corpora as you do.
The Validation Reports - be they external or internal - are an important part of your documentation. They might be the basis for any prospective user of your corpus to decided whether this corpus fullfils his/her requirements.
If there already exist any Publications with regard to the speech corpus, ask the authors to include a copy in the documentation, or list the references to them. These publications might give the user valuable insights into how the corpus may be used and what are certain characteristics of the speech data.
Any Comments of project partners, funding organization or users might be listed in the documentation as well. Be sure to ask the authors of these comments for their permission.
The Corpus History is basically a chronological list of the changes to the corpus after completion. It should name all changes of the version of the speech corpus together with the date and with what was altered in the corpus and where the updated files might be downloaded from.
Finally, since no speech corpus is absolutely error-free - there should be a List of Known Errors that have not been and probably will not be fixed for various reasons (for instance when a recording file is corrupt, but the speaker is not available any more so the recording cannot be repeated).