True. I've developed a methodology to deal with that. When me or someone else from EAI (my company) start developing a data strategy with a client, we list all the different types of data, data sources (sometimes the same data has the same sources), and relevance for the different use cases in the organization. We do this even with data that has not yet been collected (or purchased).
This is part of our data strategy program, this way companies that work with us know from the start what data they need, what they should be collecting, what are the dependencies, and their priorities! :)
Thanks for the comment, it means a lot!