One place I worked used an employee identity number that was based on two things: identifier (two decimal digits) of the component of the company which originally recruited the employee and serial number (4 decimal digits) of recruitment within that component. When I joined that company, the components were called organisations, later they were called divisions, which created no end of confusion (as previously organisations had benn split into divisions) but the personnel guys kept the numbering working just fine, and organised everyone's job title change to fit the new component names, and carried on helping with recruitment and training and so on without any noticeable disruption (that was in the days when personnel departments did useful things, before they became those useless entitities "human resource departments" who were far too important to do anything useful.