50Thus, since the pre-litigation procedure is informal in character and the parties concerned are generally acting without the assistance of a lawyer at that stage, Article 91 of the Staff Regulations is not intended to be strictly and definitively binding for the purposes of the possible contentious stage of the procedure, provided always that neither the legal basis nor the subject matter of the complaint is changed in the action brought (see, to that effect, judgments of 7 May 1986, Rihoux and Others v Commission, 52/85, EU:C:1986:199, paragraph 12, and of 23 April 2002, Campogrande v Commission, C‑62/01 P, EU:C:2002:248, paragraph 35).