In section 2.3.1, there is a note with translation issues, making it hard to understand.

"There is little market data comparing the number of pages with vertical writing mode and horizontal writing mode, but it is said that both are almost the same."
"縦組と横組の組版されたページ数を調査したデータはほとんどないが，日本における縦組と横組の本の刊行点数は，ほぼ同じくらいと予想される．"

• From "the number of pages with ~ writing mode", it is possible to interpret it as saying that the length of a book (number of pages required) will not be significantly affected if it is written vertically or horizontally. However, there is not enough market data to confirm this.
  Considering the Japanese text, this does not appear to be the intent of the note.

• The clause "日本における縦組と横組の本の刊行点数は" is missing in the translation.

For these two reasons, the English translation is unclear, and incomplete compared to the corresponding Japanese text.

Adding a verb after "the number of pages" such as 'composed' or 'typeset' could possibly help clear away the unintended interpretation.

A potential translation accounting for both of these issues could be as follows:
'There is little market data comparing the number of pages composed with vertical writing mode and horizontal writing mode, but there are said to be an almost equal number of books published for the Japanese market using each mode.'