Your research is awesome! Thanks!!!
At a guess, I could say that’s why the Harvard Law School group photographs between 1987 and 2003 are missing:
http://via.lib.harvard.edu/via/deliver/results?_collection=via&page=5
Name: William C Ayers
Birth Date: 26 Aug 1944
Address: POB 78, W Somerville, MA, 02144 (1985)
Ships that pass in the night?
http://somervillenews.typepad.com/the_somerville_news/2007/03/obama_finally_p.html
Obama attended Harvard Law School from 1988 to 1991. During his time at Harvard, Obama lived at 365 Broadway in Somerville, according to his parking tickets...