At present it is unclear at what stage or stages the various lists of Blue Book Unknowns represent initial, intermediate or final evaluations by Blue Book staff and/or Blue Book consultants such as Hynek and Battelle Memorial Institute (which carried out the March 31, 1952 – March 17, 1954, statistical study known as BB Special Report 14, and internally as Project STORK subproject PPS-100). A comprehensive examination of the sanitized and unsanitized BB microfilm files and Hynek’s enormous BB record
collection at CUFOS would be needed to answer this question in most cases but at present there are no resources to undertake such a time-consuming project. Even so, because of lost and incomplete files this may not be possible in all cases even if the available records could be studied. The goal here is completeness of documentation and to try to fill in gaps where records have been lost. Whenever a case has been evaluated as an “Unknown” or “Unidentified” by BB staff and/or competent inverstigators
it is included here, with preference given for those cases that have actually been investigated since it appears that quite a few that are on BB’s list as Unknowns do not seem to have actually been investigated. Eventually such cases will be weeded out (at the screening stage mentioned above). Cases that were evaluated by the AF as Unknowns at some point but have turned out to be IFO’s are excluded here (Fred Johnson and Chiles-Whitted are included here but with IFO notations)., and some famous cases may never have been officially considered unexplained by the military or perhaps only briefly (e.g., Kenneth Arnold).
Project BLUE BOOK UFO Unknowns (PDF)