Because they were doing it wrong.

From:  Geoffrey Hooker <[log in to unmask]>
Reply-To:  Bibliographic Framework Transition Initiative Forum
<[log in to unmask]>
Date:  Monday, May 20, 2013 4:20 PM
To:  <[log in to unmask]>
Subject:  Re: [BIBFRAME] Instance of ISBNs in MARC records

The I wonder why... series reused ISBNs for different books.

In the library where I cataloged them :
ISBN 0871974525 had eight distinct titles (9 in WorldCat)
ISBN 0871974533 had six (8 in WorldCat)

Geoffrey Hooker
It is dangerous to be right when the government is wrong. -Voltaire

On 20 May 2013 13:02, Shlomo Sanders <[log in to unmask]>
> Sorry, no numbers, but I have heard complaints of different works having the
> same ISBN.
> Thanks,
> Shlomo
> Sent from my iPad