Note: if the ISSN is recorded in the Series Statement (490 $x) then it is not necessary to record it also in 022.

Examples:

022 $a 0020-6067

022 $a 0145-0808 $z 0361-7106 $z 0027-3473
[Subfield $z contains a cancelled ISSN that is associated with the serial. Each cancelled ISSN is contained in a separate subfield $z]

022 $a 0810-8633 $y 0312-4746 (error)
[Subfield $y contains an incorrect ISSN that has been associated with the serial. Each incorrect ISSN is contained in a separate subfield $y]