Our Financial system does re-use our department numbers after some period of time, and it causes us a lot of confusion. We have faced the same issue in our HRMS only and have banned reuse of department codes to maintain historical integrity. Unfortunately for us we are almost out of codes because of many reorganizations through the years. I have come to believe that HR must have a separate organizational code that isn't a copy of the accounting charge codes. Organizational structure cannot be defined by an acctg code.
HR needs to ensure it is applied correctly to org structure.
With this approach, active records will always refer to the organization table but historical record analysis can be created using the field values stored with the record. Merging current records with old records for analysis becomes someone less complicated with this approach. If it is considered the most valuable, I suggest the 'excessive space' needed is valid. The HR organization is aimed at supporting the structure of how work is actually accomplished, which reflects all of the variations of company management structures, subsidiaries, joint ventures, committees, project teams, etc. I do disagree about the reusing of codes.