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It's tough to tell without seeing the help & marketing pages. How similar are they? Generally, these are different as marketing pages generally talk more about user benefits where help pages are more tutorial based. It's likely as long as they aren't 1:1 matches (or very close) that they can both exist. In the rare event that the help center pages are an exact duplicate of existing marketing site pages, then in theory you should be able to 404/redirect those pages and not worry about them. If there's already another version of the page on the site than there's no need to manage it in two places. Feel free to reach out if you have any questions!