Haha! No idea ... there's much about 19th century publishing which is baffling to me. Is there a date on Book 13? - if it's later than 1866 perhaps it's a revised edition with a less eccentric page order but much the same content?
Who doesn't like a good mystery?
Book 13 was published in 1857 by Phinney & Co of Buffalo, NY. Phinney & Co. moved to Buffalo in 1848 and ceased publishing under this exact name in 1862. As you undoubtedly know (but others may not), Ivison Phinney formed the Spencerian Pen Co. as a subsidiary in 1858, but I digress. Old Ivison really got around, working as/with Ivison, Blakeman & Taylor, 1846-1891 publishing dictionaries; Ivison, Phinney, Blakeman & Co., 1860-70, juvenile works; Ivison, Phinney & Co., 1846-68 juvenile works; Ivison, Blakeman & Co, 1861-91, Dictionaries as well as our beloved "Spencerian Key to Practical Penmanship"; Ivison, Blakeman, Taylor & Co., 1870-86, history, as well as the for whom the Spencerian Artistic 14 (the Principality clone) was made. Did I leave anyone out?
My Book 13 belonged to one Miss Ella L. Kellogg of Horicon, Wisconsin, whose name is written on the front flyleaf. I'm most fortunate to have one of her copy books as well (I bought them together). It's copy book #9, copyrighted 1859, of "Spencerian System of Practical Semiangular Penmanship" by Prof. P. R. Spencer (so published in his lifetime). She was a very good student--the whole book is filled out in a fair hand. This copy book was probably printed in 1862 or thereabouts, as one exercise has a date of September 21, 1862. Anyway, I ramble. I find it fun to see work done which we still copy/try to learn over 150 years later.
Probably more than you wanted to hear.