Search for authenticated ISSN records to identify which ISSN are being printed
If multiple ISSN are labeled:
add the online ISSN to subfield "a"
add the print ISSN to subfield "y"
If it is known that an ISSN is incorrect, record the ISSN in subfield "y" of the 022
Otherwise record a single ISSN you find in subfield "a" of the 022
Note $z is for a cancelled ISSN (used only by ISSN Center)