There’s the letter of the law, and then there’s the legal reality of what you’re willing to risk without getting sued, and then there’s the social reality of what you’re willing to stake your reputation on. OSM aims to be whiter than white, which sometimes means foregoing a legally plausible approach that might risk spending OSMF donations on a strategically dubious defense in court or allowing competitors to spread FUD about the project.
Many of your hypotheticals seem to rely on plausible deniability. You don’t need to live in fear that part of your brain has been indirectly contaminated by the non-free media consumption habits of friends and total strangers. Applying common knowledge is not copying. Coming along for the ride is not copying, either. However, if you intentionally use your friends to systematically extract information in bulk from a proprietary source, then even if your clean room technique technically hasn’t violated anyone’s copyright, the result may be indistinguishable from copyright infringement, inviting the same legal trouble. Besides, it would raise ethical concerns about plagiarism that will probably upset your fellow mappers.
By the way, is this purely a hypothetical question, or do you have a specific case in mind that you’d like us to consider as a community?