01X-09X Numbers and Codes (Variable Data Fields)
010 Library of Congress Control Number (NR)
012 CONSER Fixed Length Field (NR) [CONSER use only]
015 National Bibliography Number (R)
016 National Bibliographic Agency Control Number (R)
019 OCLC Control Number Cross-Reference (R) [OCLC use only]
022 International Standard Serial Number (ISSN) (NR)
025 Overseas Acquisition Number (R)
027 Standard Technical Report Number (R)
029 Other System Control Number (R) [OCLC defined]
032 Postal Registration Number (R)
034 Coded Cartographic Mathematical Data (R)
036 Original Study Number for Computer Data Files (NR)
039 Core Record Designator (NR)
044 Country of Publishing/Producing Entity Code (NR)
045 Time Period of Content (NR)
050 Library of Congress Call Number (R)
051 Library of Congress Copy, Issue, Offprint Statement (R) [LC use only]
052 Geographic Classification (R)
055 Classification Numbers Assigned in Canada (R) [LAC use only]
060 National Library of Medicine Call Number (R)
061 National Library of Medicine Copy Statement (R)
066 Character Sets Present (NR)
069 Other System Control Number (R) [OCLC defined - Obsolete]
070 National Agricultural Library Call Number (R) [NAL use only]
080 Universal Decimal Classification Number (UDC) (R)
082 Dewey Decimal Classification Number (R)
086 Government Document Classification Number (R)
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