Nichtbibliographische Identnummer
        engl.: Other Standard Identifier
   Definition: IdNr, die nicht in einem der vorgesehenen Felder untergebracht werden kann
               
               
               
               
MARC21       024     Other Standard Identifier (R)
  Subfields: 
             $a   Standard recording code
             $c   Terms of availability
             $d   Additional codes following the standard number or code
             $z   Cancelled/invalid standard code (R)
             $2   Source of code or number
             $6   Linkage

 Indic/etc.: 1st: Type of standard number or code
             0 International Standard Recording Code
             1 Universal Product Code
             2 International Standard Music Number
             3 International Article Number
             4 Serial Item and Contribution Identifier
             7 Source specified in subfield $2
             8 Unspecified type of standard number or code
             2nd: Difference indicator
             # No information provided
             0 No difference
             1 Difference