Law departments with a matter management system (aka case management system) give each matter a unique identifier matter code. That matter code can serve other purposes.
A document management system that identifies the matter for which a document is being prepared or stored, can draw on the matter code. Invoices from outside counsel need to include the matter code. Then too, if the department has a filing system, the matter code should be the key identifier for its filing structure. The matter code finds use in the records retention process, as well as in litigation support and document collection and production. Knowledge management systems might refer in their databases to unique matter codes.
Both cats and matter codes have nine lives.