Who constructs the historical record, and who mediates your access to it? Many people and institutions play a role, beginning with the people who possess the knowledge and technologies needed to produce and reproduce texts. Institutions like libraries and archives also play a role, and the present guide primarily addresses historical research in libraries. To use libraries effectively (which is to say, intentionally and systematically), you need to understand what a library is, and how it is organized, because the way in which a library organizes the historical record tends to privilege certain types of inquiry, and even to elicit certain conclusions about the past. And no, not even Google or mass digitization has been able to alter the historical record's peculiar, discursive contours, nor has it been able to fill gaps in the historical record or retrieve documents never saved. In short: your attempt to uncover overdetermination in history is itself overdetermined.
Lt. Whitman, Photographer, U.S. Naval Academy, Annapolis, Maryland: Instruction in Pistol Shooting, 1942, digitized from nitrate negative, Library of Congress Prints and Photographs Division, Farm Security Administration/Office of War Information Black-and-White Negatives