The rule that all project information must pass through the CDE at one controlled entry point, rather than being shared directly between parties by email or private folders. It sounds like a technicality, but it's what makes a CDE actually work: if a drawing can also be emailed directly to a subcontractor, there are now two versions in circulation and no way to know which one is current. A single point of entry is what keeps the CDE the genuine single source of truth instead of just one more copy of the files.