6 codes that cover most of what an originator sees. Each one carries the decision: retry or stop, how long the receiving institution has to send it, what the guidance rests on, and when it was last checked.
On a rail fact, every detail line names the section or instrument it rests on and whether that is a rule, a law, operator guidance, or observed practice.
Not yet covered: no public text sets how long after settlement a return request may be sent or how fast the receiving participant must answer; any such limit would be in the participant-only SIC Handbook; the ISO 20022 External Code Set definitions behind the six codes were not read, so meanings rest on the code names SIX prints; the SIC RTGS return request codes, which SIX recommends but does not check, are not in this directory.