“Ambivalence and Paradox: The social bonds of the public library”

In the article “Ambivalence and Paradox: The social bonds of the public library” the author, Phyllis Dain challenges the conclusions of Michael Harris, author of “The Purpose of the American Public Library: A revisionist Interpretation of History.”
Although both she and Harris deem the amount of useful historically supported facts pertaining to the creation, growth, and maintenance of the public library insufficient neither is shy in stating their interpretation of these scant facts. Her analysis of the founders and the trustees of the public library system is nonexistent; she merely states that there is a chance that Harris is incorrect in his assumptions and does not have enough corroborating evidence to support his “interpretation”.
The whole of her article is in the same vein and while she offers little or no evidence to support her stance she does ask several important questions that, if there were correlated evidentiary support for, would substantially damage the conclusions that Harris drew within his article. But it is unlikely that long work hours, manual labor and demographic instability, while historically accurate and supported, will ever be adequately linked to low library usage; very few people left written evidence as to why they chose not to make use of their libraries.

What is the minimum of historical documents needed to make an interpretation of past events? What type of documents should a historian use? Is it possible to make an accurate interpretation of any historical event or movement since we are all limited in perspective to our place, time, our moral and/or religious systems, our political and our social understandings?