Marcy Calderon refined employment income data mapping within the hmrc/income-tax-mtd-changelog repository, focusing on improving downstream data handling and reporting accuracy. She delivered a targeted configuration update to sa100_mapping_v2.csv, changing the action for Individuals Employment Income to enable more precise categorization and routing of financial details. Working primarily with CSV data and leveraging her data mapping expertise, Marcy ensured the change was fully auditable through a clear git commit. Her approach emphasized maintainable, configuration-driven data lineage, supporting future audits and cross-team collaboration. The work demonstrated careful attention to data structure and process discipline over the course of the month.