According to Wikipedia, “...Bowker provides bibliographic information on published works to the book trade, including publishers, booksellers, libraries, and individuals... Bowker is the exclusive U.S. agent for issuing International Standard Book Numbers (ISBNs), a universal method of identifying books in print.” (https://en.wikipedia.org/wiki/R.R._Bowker, accessed July 31, 2015)
Additional books are classified under “non-traditional” or “unclassified;” these are not included in this chart. These ISBNs ranged in count from 247,777 to 2,042,840 per year during this ten-year period.