Public companies who publish their roadmaps have lots of legalese in them: "Don't rely too heavily on this document, please!" But even if your roadmap is only shared internally, a disclaimer is useful.
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It won’t actually provide a lot of protection against accusations of broken promises, but it will help set the expectation with your customers and stakeholders that the roadmap will continue to evolve based on input from them and other customers like them. Play it up. Make it into a benefit!
I talk disclaimers in Chapter 2 of my book Product Roadmaps Relaunched. What are yours? Discuss.