Google has claimed that about 130 million books have been published (that factoid is all over the web). The number of 10-digit ISBNs is 1000 million (there's a check digit) and people have only just started using 13-digit ISBNs that start with 979 instead of 978; but of course there must be lots of wasted ISBNs, for example when a publisher optimistically buys a big block and then goes bankrupt. Both those numbers suggest that the "ISBNdb" with less than 31 million ISBNs is far from complete.
The frequency of each top-level prefix (which tells you the geographical or language region) would be interesting. That would the first thing I'd calculate if I had the data on my disc.
The frequency of each top-level prefix (which tells you the geographical or language region) would be interesting. That would the first thing I'd calculate if I had the data on my disc.