Documentation should be complete and signed off before the first bit of code is written.
naah, the requirements document should be complete and signed off before the first bit of code is written.

There is a difference.

The documentation is for the end user, the requirements document is for system design and nothing can be documented before the system design is completed.

If tech writers are required to "read the code"
never heard of that one, there are many names for what they are "required to read", I call it a "documentation template"

Erik