...
When we move to implementation (either after the design phase is completed or in parallel) we can add extra test cases as needed. Again these test cases can test existing requirement or add new ones.
This can happen all the way down to the bug fixing phase.
Once the feature is complete we should have a set of test scripts which represent both the requirements, test plan and parts of the design.
...
However, my argument is that the above process can alleviate much of the maintenance of the documents required.
Lets Let's take the Requirements document as an example.
...