At present there are 172 publication records with ISBN13s that start with "294". These numbers are only usable on www.bn.com though can also be used on cataloging sites such as Goodreads. They are currently known as informally BN IDs (Barnes and Noble IDs)[1] and are similar to Amazon's ASIN (Amazon Standard Identification Number).
The feature request is 1) Add support for links to www.bn.com in the "Other Sites" part of the publication display and 2) that the Amazon sites not be linked as these ISBNs should never work on Amazon's sites. Sites other than the Amazon ones would need to be checked to see if there's a possibility of a BN ID being used on those sites.
This link can be used to view the current publication records with BNIDs: http://www.isfdb.org/cgi-bin/adv_search_results.cgi?USE_1=pub_isbn&OPERATOR_1=starts_with&TERM_1=294&ORDERBY=pub_title&TYPE=Publication
[1] While Amazon documents the term ASIN I was unable to find anything on www.bn.com that defines or explains the BN ID. They use "BN ID" on their pages of ebooks for sale. Apparently there's an API available but only for their marketplace vendors. The API documentation seems to be under NDA and so is not public.
Anonymous
The BN IDs which were originally entered as ISBNs have been moved to the External ID field. No other software changes are necessary. Closing the FR.