The brief lives as a stand-alone page. Without the Briefs database, the Select properties are not available, no Relation can point at the brief, and no Rollup can aggregate against it. The brief becomes a doc that only full-text search reaches. Move briefs into a database before any other pattern matters.
Artifacts created without the Brief Relation. Someone drops a quick page into the Pages database without setting Brief, and the artifact disappears from every brief view. Make Brief a required property on the artifact database (Notion supports required properties on database creation forms via templates). Add a hygiene view that surfaces orphaned artifacts.
Multiple briefs without distinguishing properties. The team accumulates ten briefs all titled with the project name, all at Status = Active, no Owner. The workspace cannot tell which brief is current for which surface. Keep Status disciplined (one Active per surface), require Owner, and use a Multi-select Surface property if multiple briefs cover different surfaces of the same product.
Notion-as-CMS habits override Notion-as-spec patterns. The team treats the brief like a published page (lots of formatting, hero image, embedded video) rather than a structured row. The result is briefs that look great and aggregate poorly. Keep the brief schema-first; the prose lives inside the page body, but the queryable data lives in properties.