It was announced on January 24, 2004:
On Wed, May 1, 2013 at 9:06 AM, Bigwood, David <[log in to unmask]>wrote:
> On Catalogablog there is an posting on Tuesday, September 21, 2004.
> David Bigwood
> -----Original Message-----
> From: Code for Libraries [mailto:[log in to unmask]] On Behalf Of
> David J. Fiander
> Sent: Wednesday, May 01, 2013 10:35 AM
> To: [log in to unmask]
> Subject: [CODE4LIB] When did OCLC's original xISBN service launch?
> According to the Code4Lib mailing list archives, the service moved from
> "experimental" to production, and changed format, in February, 2007, but
> the earliest reference to the service in the archives is a question from
> Thom Hickey in May, 2005 soliciting feedback about what additional
> features might be of interest.
> - David