When the original poster forwarded the reply from the publisher, I was assuming the phrase "we have been told" was referring to the UK ISSN Center (but I may be wrong here).  Thank you Regina for checking.

Steve Shadle/Serials Access Librarian  *****  shadle@u.washington.edu
University of Washington Libraries      ***     Phone: (206) 685-3983
Seattle, WA 98195-2900                   *        Fax: (206) 543-0854

On Wed, 23 Jan 2008, Regina Reynolds wrote:

> Peter,
>
> I would concur with Steve Shadle's interpretation (almost always do!) but
> will also send an email to the UK ISSN Centre to confirm their decision,
> since no variant title was added to the ISSN Portal record, as I would
> have expected if the UK Centre had follwed through on their decision to
> treat the change as a minor one.  It is entirely possible that updated
> record has not yet been sent for inclusion in the Portal but just in case
> this has not been done, I'll check into it.
>
> Regina Reynolds
>
>
> On Wed, 23 Jan 2008, Steven C Shadle wrote:
>
>> I would consider dropping of the word 'supplement' to be the dropping of a resource type word and covered as a minor change in AACR2 21.2C2b)ix)

>>> Dear Peter
>>>
>>> Thank you for your enquiry but we have been told that as we have amended
>>> rather than changed our title completely a new ISSN isn't necessary.
>>>
>>> Best wishes
>>> Gerard