523 Time Period of Content Note (CF) [obsolete]:

Field 523 was made obsolete in 1993. Both indicator positions were undefined. The subfield codes were: $a (Time period of content note), $b (Dates of data collection note), $6 (Linkage). Data previously recorded in this field is now recorded in field 500 (General Note) , field 513 (Type of Report and Period Covered Note) , subfield $b (Period covered), or field 518 (Date/Time and Place of an Event Note) .