Wind and solar curtailment in Brazil exceeded 10 TWh in 2024, but only cuts classified by the system operator as electric/external-unavailability reasons (REL) are reimbursable, and the regulator is currently revising the rules that define the cut categories. This paper provides the first event-level link between transmission disturbances and renewable curtailment in the Brazilian Interconnected System. We structure the complete set of 853 disturbance bulletins (BISE) issued by the ONS between 2012 and 2026 and connect each event to the official half-hourly plant-level constrained-off records under a conservative rule: a plant enters an event only if curtailed at the disturbance onset, the onset reason defines its category, and only same-reason cuts accumulate over the event window. Of the 194 disturbances in the period with public curtailment data, 41% show no curtailment response and 23% coincide with REL cuts. Around the onset, REL cuts peak exactly at t_0 and decay within hours, while reliability (CNF) and energy-surplus (ENE) cuts do not, indicating that the reason classification is empirically identifiable. Valuing attributed cuts at the hourly spot price yields 172 GWh and R$ 20.8 million of REL curtailment in the six hours following the 159 isolated events, out of 944 GWh and R$ 147.8 million across all categories. We also find that 30% of the bulletins lack a defined cause, and that the official severity index (GIE) does not register generation-side impacts.