Somehow, I think it was inevitable that a determinedly analytical mind like Lynn Thorndike's would have left a well-organized archival record: and so it was that he and his successors left his extensive collection of papers to the University of Columbia, the last place he worked as a History Professor. The archival finding aid went online here only in 2004, so it seems likely that few historians have thought of using it.
All the same, it still comes as a bit of a surprise to find out that there are 60 linear feet of records in this archive ("ca. 30,000 items in 124 boxes and 1 Flatbox; some in Mapcase"). As well as containing the obvious stuff such as correspondence and numerous card files, this also includes "76 volumes of personal diaries, 1902-1963".
Thorndike's epic quest to examine, read and understand medieval scientific texts was on a scale few have attempted before or since: his multi-volume "History of Magic & Experimental Science" provides a richly textured background that I think anyone seriously looking at early modern proto-scientific mysteries (such as the Voynich Manuscript, naturally) should have gone through. And even so, how much more might there be languishing in his papers - unseen, unread, unknown to us all?