Having the incorrect ISSN's in |y and |z subfields of 022's sounds like a
good idea.  However, here in the Florida SUS, we use a version of NOTIS
as enhanced by our own FCLA.  Recently they brought up a
"hook-to-holdings" feature that matches citations from on-line indexes to
bibliographic records in the on-line catalog--based on ISSN's (and
ISBN's).  One of the problems they encountered were false matches on
ISSN's in |z and |y subfields.  So... they de-indexed these subfields.
So much for noting incorrect ISSN's in your on-line catalog.

James D. Michael
Cataloging Department - LIB 020H
University of South Florida Library
Tampa, Florida 33620
(813)-974-2453
JMICHAEL@LIB.USF.EDU