This short piece provides the cumulative textual evidence that Pynchon consulted a single source, Golder, F.A., 1915. "The Russian Fleet and the Civil War". The American Historical Review, 20(4), pp.801-812, to construct the historicity of the Peter Pinguid Society episode in The Crying of Lot 49, as opposed to consulting the original Arkhiv Morskogo Ministerstva, Dielo Kantseliarii Morskogo Ministerstva, no. 91, pt. III., pp. 102, 103.
As a brief aside on this issue of Pynchon Notes; it appears backdated. My submission was made in 2010 and the final copies have just arrived, December 2011, but if you are looking to consult, the date of publication is listed as Spring-Fall 2009.
The full text of the article is available for download: Martin Paul Eve - Historical Sources for Thomas Pynchon's Peter Pinguid Society - 2010.