DSE is so far doing a weak job of relating documents for me. I have a folder containing six documents (searchable PDFs and TextEdit RTFs), all dealing with a planned trip to Alaska, all the same date, five of the filenames starting with the same two words (the name of the cruise line), all with much content in common. If I drag one of the documents into DSE, “See Also” shows only one of the other five - the same one - for 4 of the documents. For two of the documents, See Also shows 2 of the other documents - the same one and another. Interestingly, when that one document that appears in See Also for the other five is dragged into DSE, none of the other five appear in See Also: only that file itself. In some of the cases, See Also additionally shows a relevant Contact, relevant email, or other documents less closely related.
That is, considering only the six documents in this folder:
for documents A, D, E, and F, See Also shows only A; for document B, See Also shows A and C;for document C, See Also shows A and B.
See Also does have multiple lines showing many locations of the related email and reply: Is there a way to stop that?