Michael Adams wrote:

Unopened pages in older books are simply the result of those
particular folds missing the trimming knife.

Agreed, except that frequently there was no trimming knife and books were
simply marketed without opening the pages.

This book has been
deliberately produced with uncut edges on two sides.

Yes, it looks that way (http://www.ehistorybuff.com/eisenhowerbk.html).

Its impossible to fold a sheet of book paper so the
folds only occur on two edges of the finished book.

It's not impossible at all. It just depends on how many times the sheet has
been folded. A folio volume is made of sheets that have been folded once;
all three adges will be free of folds. A quarto is made of sheets which have
been folded twice; one edge (the top edge by convention, but it could
equally well be the bottom) will be folded. An octavo is made of sheets
which have been folded three times; two edges (the fore-edge and the top or,
possibly, bottom) will contain folds. The third edge will not contain any
folds.

To be bound in this way, the original sheet would have to be printed
lengthwise, with, from left to right, pages 5, 12, 9 and 8 upside down at
the top and 5, 12, 9 and 8 right-way up at the bottom on one side of the
sheet, and pages 7, 10, 11 and 6 upside down at the top and 2, 15, 14 and 3
right-way up at the bottom on the other side.

Try it; take a piece of A4 paper, fold it in half, then again and once again
(always
folding lengthwise). This makes eight leaves of paper. On one of the longer
sides each leaf is connected to another via one central fold. This side will
be at the spine of the book, where the signatures are sewn. The other longer
side will have four leaves that are separated followed by four unseparated
ones. This side is the front edge of the book. One of the shorter sides
consists of two sets of four leaves each connected by a fold. The other side
has no folds.

16mo consists of a sheet folded in half twice, then in thirds, and again the
finished book will have folds on only two sides (the fore-edge and -
normally - the top). 24mo consists of a sheet folded four times, and has
folds on all three edges.

Of course, there are many variations on these basic folds, but the point is
that in principle it is perfectly possible for a book to have unopened or
uncut bottom and fore-edges and be perfectly smooth *from the beginning* at
the top (since that edge consists only of edge parts of the original sheet,
with no folds).


--
John
http://rarebooksinjapan.com