Are real world software engineering/design docs available for study

Are there any real world software engineering/design/requirements documents available. Most text books on the topic make use of fictional/toy documents which are not very helpful in converting which details are important to include and which are not.

More over good exemplary documents are valuable guides in how to go about creating such documents.

Certainly good documents have been produced in the last 50-60 years. Are they all lost to history?