How Report Formation Shapes Evidence Use in Multi-Agent Reasoning

Giving a final language model every source document may seem to make evidence sharing among upstream agents redundant. We test this assumption by varying source access during report formation while fixing the final sources and the agents' initial answers and confidence values. Across 249 task variants from 128 synthetic decision scenarios, sharing during a report update improves final accuracy by 18.36 percentage points. We exchange naturally generated explanation records, statements relating cited passages, independently of their automatically copied source text. Explanations formed after sharing improve accuracy by 13.48 points under fixed copies. Thus sharing changes useful report content beyond the source passages explicitly repeated for the final model. We next retain the earlier report and supply a correct, reference-derived judgment of whether a rule applies to the current case. This diagnostic revision improves decisions, although the predicted reverse effect of leaving applicability unresolved is not established. Finally, both a correct and an unresolved interpretation remain present at matched positions. Designating the correct interpretation as the report's current judgment rather than an unincorporated external annotation improves accuracy by 9.18 points. Benchmark studies examine relevance under separately specified information controls. Together, these interventions show that complete final access leaves report formation consequential: generated explanations and their assigned report roles affect how available evidence is used.