Unique FTRs help distinguish one external output from another. An FTR must be either an Internal Logical File and/or External Interface File.
The elementary process associated with an external output may update an internal logical file or external interface file. For example, the elementary process that produces as payroll check may include an update to a file to set a flag to indicate that the payroll check was produced. This is not the same as maintaining the file. Maintained is the process of modifying data (adding, changed and deleting) via an elementary process (via an External Input). The primary intent of an EO is not to maintain an ILF.