When Field History Tracking is enabled for an object, users may report that only some of the fields selected for tracking are included in the record's history-related list on record creation.
This is expected behavior and by design.
By default, field history tracking in Salesforce products is only expected to create an entry to track the user and the date/time of record creation.
Field history tracking entries for other tracked fields are only created when field values are changed or modified. Inputting a field value when creating a new record does not constitute a change or modification to the field's value. Record data for tracked fields on record creation are not expected to be captured in the history-related list by default.
However, if your organization has created automation that's invoked on record creation, such as Apex, Flow, Processes, or Workflow and they perform Data Manipulation Language (DML) operations or input values into tracked fields, those field values will also be included in the history tracking for record creation.
Depending on how the records were created or modified, the effect is scenarios where users find that some but not all data input into fields that are selected for history tracking are included in the history-related list for the record creation entry.
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