This information, which can be found in some form on nearly every card, refers to correspondence folders that were probably kept in the IRO Control Centers. Unfortunately, it is not clear exactly which folders are being referred to by these letters (such as DF, M, K, T, MP and MK) and numbers. However, the “Record destroyed” stamp suggests that the folders listed here no longer exist. References to a Mappe or folder can sometimes be found on the CM/1 applications as well.