...
The Harvard Library uses a 914 NO-WORLDCAT field in bibliographic records to designate the record as unsuitable for sharing in OCLC. The two most common reasons to use the 914 field are: 1) sparse bibliographic information, and 2) coding problems which could cause duplicates in Data Sync. If the 914 field is present, the record will not be reported to OCLC via the OCLC Data Sync process. Consult the updated the Metadata Standards Working Group's Best Practice for Use of Field 914 for details.
At Houghton, this process will generally occur at the Acquisitions Unit when accessioning a new acquisition and no viable OCLC record is available requiring a brief preliminary Alma record to be created.
UPDATE (June 2020):
As of June 9, 2020, LTS has instituted Alma Brief Level rules allowing Alma to automatically exclude records from publishing in OCLC if they lack certain elements (see Alma Brief Levels wiki page). However, if a record is exported from OCLC into Alma during the acquisitions process (i.e., awaiting full cataloging), the existence of OCLC number in the record trumps the criteria listed for exclusion and that particular record will push out to OCLC during the iterative Data Sync process. In that instance, you will still need to include 914 manually if the item is awaiting full cataloging. Once the item is fully cataloged, 914 should be removed from the bib record by the cataloger.
...
Starting April 13, 2020, Harvard Libraries will be implementing the use of new MARC field 914 in bib records as part of the OCLC Data Sync project. This new field will prevent a bib from being reported to OCLC through Data Sync and will replace the use of 908 in holdings. Houghton will adhere to this practice and discontinue the use of 908 in holdings while adding 914 to bib records moving forward.
...