Errors in ISBNs

The ISBNs (International Standard Book Numbers) of Thomas and Webb, Butterflies of Dorset, are seriously muddled.

The UK ISBN Agency's database shows

0-900341-20-3 978-0-900341-20-5 Butterflies of Dorset (hardback)
0-900341-21-1 978-0-900341-21-2 Butterflies of Dorset (paperback)

The back cover, of both editions, shows

The verso of the title-page, of both editions, shows
0-900341-20-1 pbk (an invalid number)

Correcting this complex error would be difficult, and as it has stood for some 30 years without apparent problems I have left it alone.

John Palmer, 2014-02-05