As a Product Manager, your job is to document and clarify and share every bit of thinking with the rest of the team. It is not just the spec, but how it evolves, why it evolves the way it does, how each interaction with the team and potential users, shifts it a bit.
I like this part from the book 42 Rules of Marketing:
Your job is to document, document,document, and then go back and clarify, clarify, clarify.
Your PRDs (product requirements documents) and MRDs (market requirements documents) should be the go-to information sources for everyone working on the product or supporting the product in some way.
I will go one step further. Instead of creating a large PRD, MRD, use an internal Wiki, blog or some other tool that lets people see the evolution of your thought process and participate, question and make suggestions. I think how you start out, how and why you change your requirements, is almost as illuminating as the requirement itself. Listing various hypotheses that need to be verified may be another useful outcome of this whole exercise.