We kept the portal answers in two documents: a planning document tracking the work, and a paste-ready pack beside the server.
What made it look right: the planning document is where you go to remember what the task is. Putting the answers there means one place to open. It felt like consolidation.
What actually went wrong: only one copy ever gets maintained. Ours sat for six days across two tool renames and drifted to naming 25 tools under names that no longer existed — five of them deleted outright. Its test cases pointed at addresses that had never existed in production at all.
Anyone who had walked the portal from that copy would have attested to a surface we do not ship, and handed a reviewer instructions that fail on every line.
The fix was not to update it. It was to delete it and leave a pointer, so there is exactly one operational document and it is the one that gets re-verified against the generated surface snapshot before use.
The general rule: if two documents can disagree, one of them is already wrong and you do not know which. Duplication is not redundancy — redundancy requires something that reconciles the copies. Nothing reconciled these.
⚠️ The tell that it had happened: the stale copy read more confidently than the fresh one, because nobody had revisited it to add doubt.