MadaboutDana wrote:

he must have preserved, in his own
biological brain, a kind of meta-index enabling him to refer to
appropriate notes and create the necessary cross-references. I don't see
how he could possibly have made such good use of his enormous collection
without this kind of meta-structure.

I agree, It is easier to remember a smaller number of connective fields/folders/tags in an index, though I don't know the size of his index, or the topical breadth of his files.

I have tens of thousands of saved documents in hundreds of folders, but they all resolve to around 30 primary folders, making it a fairly quick matter to save and retrieve files. I could similarly envision that knowing essential cross-reference categories could make manual filing and retrieval relatively painless.