In case UPC_CFI_363/2023, the Local Division Düsseldorf recently provided helpful clarification for multi-party litigation. The decision is dealing with a case in which a claimant chose to sue multiple defendants – alleged infringers - in a single suit. According to the LD Düsseldorf, each defendant maintains their independence in the proceedings, ensuring that actions by one do not prejudice others.
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The independence of the individual proceedings means that defendants must individually decide their course of action, be it challenging the patent's validity or contesting infringement claims, without relying on co-defendants' actions.
According to the LD Düsseldorf, Rule 25.1 of the Rules of Procedure (RoP) requires that if a defence includes the claim that the allegedly infringed patent is invalid, each defendant must individually file a counterclaim for the patent’s annulment. However, this does not preclude multiple defendants from jointly filing such a counterclaim. If, however, some defendants choose not to file a counterclaim for annulment, and thus the counterclaim is explicitly filed only by some, the defendants not involved in the annulment counterclaim are formally excluded from arguing the patent's invalidity in their proceedings. Therefore, they cannot successfully argue the lack of legal validity in their case. However, as long as the court does not separate the proceedings against multiple defendants, this has no practical effect.
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