OCLC sends enhanced records when certain criteria have been met triggering the delivery, such as the addition of a Formatted Contents field, an upgrade to Resource Description and Access or an increase in the encoding level. These updates can appear as soon as the day after holdings have been attached. When an existing record in the database has been overlaid with an upgraded version of the record in this way, there will be a [local processing field] identifying it as an OCLC Record Update. That note will frequently be followed by a [different locally defined field] describing the reason for the record update. We retain local edits noted in the [yet another local field] of the record to be replaced