088 Subfield $z - Canceled/invalid report number:

Subfield $z contains a canceled or invalid report number. Each canceled or invalid report number is contained in a separate subfield $z. If no valid report number exists, only subfield $z should be recorded.

Examples:

088 ##$aNASA-RP-1124-REV-3$zNASA-RP-1124-REV-2

[One valid report number has been canceled in favor of another.]

088 ##$zNASA-TN-D-8008

[Report number is invalid due to an error in assignment or printing on the item.]