Either commit to keeping documentation rigorously up to date, or save yourself the effort to write it. With code it's easy: keep the documentation in the same repository as your code and make documentation an integral part of the review process.
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But with that approach the only right thing to do is to delay documentation until the software is dead stable, unmaintained, unsupported. You raise an important point, but I believe this is a concern orthogonal with respects to documentation (continues).
No, I don't think there's that constraint: I propose coding and documenting in parallel, and independently. Release the code when it's ready, and keep releasing the docs continuously for all versions you care about. Tools should help with this, though.