The rationale behind the MR/AP coding systems created by the Appeals Department is unclear, although they appear to be mainly chronological and often thematic. Some reports were allocated a MR number and later received an AP number as well - these have been catalogued under their original MR number. Reports that only had an AP number have been catalogued under this number. Reports that had neither an MR or an AP number have been catalogued chronologically at the end of the series.