Why Formula Fields Are Not Visible for Reports in Vault?
To measure a value that can only be derived from a combination of multiple fields or by analyzing the history of field values, users can create a special formula-type field and use it in reports.
A formula field is configured with the the following formula:
dateDiff(firstTimeInValue(Document.status__v,"Draft"),firstTimeInValue(Document.status__v,"Approved for Distribution"))
It is not visible in the Filters, Conditions, or Columns in reports if the Include previous document versions option is selected.
This is an audit trail formula field for Documents that is only supported at the Document level and not at the version level. Hence, when the Include previous document versions option is selected, the field does not appear in reports.
Vault Help Documentation: Creating Custom Reporting Metrics with Formula Fields