What happens when the end of a document numbering sequence is reached in Vault?
When the end of the current document numbering sequence is reached in Vault, the sequence expands on its own. This is done when the next document is created that is classified by the document type that uses this sequence.
Example: A document number of a document uses the naming convention of PP-US-XXXX. When the number reaches PP-US-9999, the next document that is loaded into Vault using that naming convention is named PP-US-10000.
Vault Field Documentation: Managing Document Numbering