Situation, a department head left the company. The company is looking for a replacement by advertising the position and hiring a head hunter. Unfortunately this didn't work out (so far) and the position is unfilled for more than two years. During that time the former deputy department head is acting as department head. If the deputy is on holidays or otherwise unavailable there is a temporary void in responsibility.
The company is located in Germany and has a Betriebsrat or works council. This is an elected body from the employees tasked with representing the interests of the employees towards the company leadership. The Betriebsrat has various legal rights concerning the advertising of the position and can even refuse to agree to the hiring of a specific person if there are good reasons for that.
The deputy department head has been doing the job of a department head for two years without getting the corresponding pay increase. If they were officially declared the new department head that would also entail that there is a new deputy department head which would also come with a pay raise.
Question: Does the Betriebsrat has any rights in this situation or does the employer already do what they have to just by advertising the position even if that is unsuccessful?