A case note says what happened. A decision record says why it was reasonable at the time. Capture the question, the evidence that mattered, what you ruled out, the outcome and why, the scope and date, and the status. For the thinking behind this, read AML teams keep the cases and lose the reasoning.
Companion slides: https://speakerdeck.com/technoxander47/old-decision-new-case-reuse-test
A related matrix: https://www.tumblr.com/vop25/832421899455905792/when-can-yesterdays-judgement-help-todays-alert?source=share
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