The relevant passage tells how FELLOWSHIP OF THE RING ends
with "the fall of Boromir to the lure of the Ring; with the escape and
disappearance of Frodo and his servant Samwise; and the scattering
of the remainder of the Fellowship by a sudden attack of orc-soldiers,
some in the service of the Dark Lord of Mordor, some of the traitor
Saruman of Isengard. The Quest of the Ring-bearer seemed already
overtaken by disaster" (TT.9-10)
What's remarkable is the passage I've marked for emphasis. Here in the summary of Volume I we are told things the reader could not learn by reading FELLOWSHIP, indeed not until the opening pages of Volume II: that the Fellowship has been attacked by orcs. This information is not within the last chapter of the previous book, which ends with the Fellowship scattering, running off in all directions. And it's later yet, though still in the first chapter of TWO TOWERS, that the survivors figure out the orc-band has divided loyalties between Mordor and Isengard.
I think it's extraordinary that Tolkien wd include in a summary information not contained in the thing being summarized (in this case, Volume I of LotR). Thinking the synopsis might have been put together by someone at Allen & Unwin, years ago I wrote to Rayner Unwin with a query, asking who had written these synopses: someone at A&U or Tolkien himself. Mr Unwin kindly replied, saying that it was of course Tolkien himself.*
So there it is: Tolkien's synopsis contains information not in the thing being synopsized,
Given how carefully Tolkien seeds information within his tale and how carefully he doles it out when the time comes, I have to conclude this is entirely deliberate on his part, I assume to heighten the drama of the second volume's in medias res opening.
I suspect this has gotten such little attention because most of us come to TWO TOWERS fresh from having just finished FELLOWSHIP and plunge right in, having no need for a synopsis of the book we just finished devouring for the dozenth time. In any case, obviously this is a minor point (or otherwise I wd have seen somebody else mention it in all these years). But it remains a bit of a puzzle, to me at least.
current reading: Barlow's COLUMBIAD (1807). finished with the poem and on to the (extensive) endnotes; the author's efforts to explain what he's talking about take up about 20% of the whole.
*as confirmation of this, Archivist Bill Fliss points out to me that Marquette holds Tolkien's typescript of both pieces: 3/5/26 (TT) and 3/7/49 (RK).