[Koha] ISBN - must they be unique?

[Elaine Bradtke]

In the process of cleaning up data to prepare for a batch upload into
Koha, I have noticed that some of our ISBNs are not unique.  These are
books from small independent publishers who forgot to change the ISBN
when they issued a new book.   I'm happy to leave them in the ISBN
field (020a ) as long as this won't cause problems in Koha.   Looking
at the framework it is also tagged as  biblioitems.isbn.  I know
record matching uses ISBN. Does anyone know if the contents of this
field must be unique?
Thanks
-- 
Elaine Bradtke
Data Wrangler
VWML
English Folk Dance and Song Society | http://www.efdss.org
Cecil Sharp House, 2 Regent's Park Road, London NW1 7AY
Tel    +44 (0) 20 7485 2206 (This number is for the English Folk Dance
and Song Society in London, England. If you wish to phone me
personally, send an e-mail first. I work off site)
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Registered Company No. 297142
Charity Registered in England and Wales No. 305999
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"Writing about music is like dancing about architecture"
--Elvis Costello (Musician magazine No. 60 (October 1983), p. 52)