Saw your post on the Koha list. Some publishers have indeed prepended 978 to their shorter ISBNs but for other publishers, the 13 and 10 digit ISBNs are different, so your matching rule would not work well. For example, the book Running with Scissors: *ISBN-10:* 0312938853 *ISBN-13:* 978-0312938857 Add to that the problem of having multiple ISSNs in many records. Some OCLC records for a book will list in the the hardback, paperback, cased set, and ebook ISBNs all in 020$a fields for one of those versions. Some ebook vendor-supplied records put the hardcover ISBN in the 020$a and don't list the electronic version's ISBN at all. Which is to say, the 3 digit offset is not going to work well at all. Happy Boxing Day! -- Stacy Pober Information Alchemist Manhattan College Library Riverdale, NY 10471 stacy.pober@manhattan.edu