Supplementary records definition including break down of areas in the definition. Analyzing the definition of key term often provides more insight about concepts. Supplementary records can be defined as: Information outside the usual accounting record; also called supplemental records. Supplementary records are records outside the normal process. We may keep supplemental records about customers, employees, or vendors, supplemental records that help us deal with these individual. We may keep supplemental records about how a process could potentially be improved.