A useful shared reference records the decisions people need for the next brief. The important questions are what belongs in it, who keeps it current and how the team uses it.
Repeated reconstruction creates variation
When core decisions are not stored clearly, every brief must reconstruct the audience, offer, evidence, objections and desired action. That reconstruction depends on memory and whoever happens to be involved.
A source of truth governs decisions, not just files
A useful source of truth is not a large folder containing every document. It identifies which information is approved, what each claim is based on, which assets are current and where uncertainty remains.
Consistency does not require identical outputs
A website, advertisement, sales conversation and article serve different purposes. They should not repeat wording mechanically, but they should return to the same approved understanding of the offer, audience, proof and boundaries.
What the shared foundation should clarify
It should clarify the audience, problem, offer boundaries, approved claims, supporting evidence, objections, next actions, governing visual and verbal decisions, and what still requires human approval.
Governance matters as much as storage
A source of truth becomes unreliable if no one knows who can change it, how changes are approved or whether old information remains in circulation. Ownership, provenance and review are part of the system.
When the problem is larger than one page or campaign
If several marketing activities keep becoming disconnected, repairing them one at a time may offer temporary relief without addressing the cause. That conclusion should follow investigation, because not every inconsistency requires a complete system.
Conclusion
A shared source of truth reduces accidental drift so the business can adapt without repeatedly losing the meaning it is trying to express.