Number 9 was printed after number 17 - https://www.librarything.com/nseries/81668/Computer-Monograp... (Click on publication) 11 might have been a place holder that didn't make it.
You can try searching the editor on the internet archive - https://archive.org/details/inlibrary?tab=collection&query=%... or the publishers "London, Macdonald and Co.; New York, American Elsevier" or in "The British National Bibliography cumulated index, 1968-1970" https://archive.org/details/britishnationalb0000unse_x4v2/pa... (The "who is related to whom" might be a typo)
Number 9 was printed after number 17 - https://www.librarything.com/nseries/81668/Computer-Monograp... (Click on publication) 11 might have been a place holder that didn't make it.
You can try searching the editor on the internet archive - https://archive.org/details/inlibrary?tab=collection&query=%... or the publishers "London, Macdonald and Co.; New York, American Elsevier" or in "The British National Bibliography cumulated index, 1968-1970" https://archive.org/details/britishnationalb0000unse_x4v2/pa... (The "who is related to whom" might be a typo)