This folder contains correspondence and other documents that were probably generated during the period 1887-1898 but for which no specific year can reasonably be conjectured. Some of these documents may have been generated as early as 1880, and a few as late as 1899. Included are items that were removed from the main run of dated folders because the evidence indicated that they had been incorrectly filed. Other material, recently processed into the Document File, is filed in this folder in order to avoid an arbitrary, and perhaps erroneous, attribution of a year. Remaining within the main run of dated folders are undated documents that were likely generated within the year of attribution, along with others that present no compelling evidence of being misfiled. In such cases, the undated items appear at the end of the folder, following the dated documents. Readers should be aware that some of this undated material may not be filed under the correct year.

Among the undated documents in this folder are items regarding the commercial and technical development of the telegraph and the phonograph. Included are two lengthy manuscripts by Edison, ca. 1888-1892, regarding the proper operation and maintenance of the phonograph. Galley proofs [not selected] of the 74-page manuscript, with annotations by Charles Batchelor, can be found in the oversize Document File. There are also documents pertaining to the controversy over alternating current. Other letters relate to Edison's personal and business finances. Among the correspondents are Edison associates Edward H. Johnson, Ezra T. Gilliland, Grosvenor P. Lowrey, and W. Grylls Adams.

A probable range of years has been conjectured for each document, and the items appear in chronological order according to the first year in the range. In cases where several ranges begin with the same year, the items are sub-organized chronologically according to the second year in the range.

Approximately 30 percent of the documents have been selected. Categories of documents not selected include routine correspondence about meetings; routine items relating to supplies, shipping, and inventories; and other documents of a non-substantive or fragmentary character. Also not selected is a multi-page cipher key for electric light system orders.