The OCLC-MARC Bibliographic, Authority, and Holdings Format Update 2019 is scheduled to be installed soon.  All details are now available in OCLC Technical Bulletin 269:  OCLC-MARC Format Update 2019 available at  This update will implement MARC 21 format changes announced in MARC 21 Update No. 27 (November 2018;, including:
Additionally, OCLC will validate MARC codes announced in two Library of Congress Technical Notices ( issued on February 8 and March 27, 2019.
Although MARC 21 Authority Format changes From Update No. 27 are documented in Technical Bulletin 269, the Authority record changes will be implemented not at this time but instead at a future date in coordination with the Library of Congress and the Name Authority Cooperative (NACO) of the Program for Cooperative Cataloging (PCC).  LC, NACO, and OCLC will make announcements at that future date.
Changes to Control Subfield $6 announced in the Bibliographic, Authority, and Holdings format Update No. 27 will not be implemented at this time.  Control Subfield $6 has not been implemented in the OCLC-MARC Authority or OCLC-MARC Holdings format.  OCLC-MARC Bibliographic Control Subfield $6 already accommodates the four-alphabetic-character values documented in ISO 15924; the standard’s three- digit numerical values are not currently accommodated.  Where subfield $6 has been implemented in OCLC-MARC, the subfield is always system-supplied, is never created manually, and does not appear in online displays. As such, accommodation of the ISO 15924 three-digit numerical values within WorldCat remains under consideration.
OCLC plans to install the OCLC-MARC Bibliographic, Authority, and Holdings Format Update 2019 soon and will make announcements widely through the usual discussion lists and Connexion logon greetings at that time. 
Please forgive any duplication of this message.
Jay Weitz
OCLC · Senior Consulting Database Specialist, WorldCat Metadata Quality, Global Product Management
6565 Kilgour Place, Dublin, Ohio USA 43017
T +1-614-764-6156 · T +1-800-848-5878 x6156 · F +1-614-718-7195 · Blog · Facebook · Twitter · YouTube