MYTH: "Just keep one source of truth."

MYTH: "Just keep one source of truth."
The correction: declaring a single source doesn't make the other five copies disappear. You need a written rule for which doc wins and where the others must point.

SOP: Establishing source-of-truth
Run this whenever the same fact lives in two places.

Stage 1 — Pick
— ☐ Name the one canonical location for this fact. (Owner: data owner)
— ☐ Write why it wins, so nobody re-litigates it. (Owner: data owner)

Stage 2 — Redirect
— ☐ Replace every duplicate with a link to the canonical source. (Owner: data owner)
— ☐ Where a copy must exist, add "synced from [source], do not edit here." (Owner: data owner)

Stage 3 — Maintain
— ☐ Name who updates the canonical source and how often. (Owner: data owner)

Owner: data owner. Trigger: a fact appears in two docs. Done-when: one source holds the value, the rest link to it.

Save this. Run it every time.