SI(((Date>=B5)*(Date<SI(C5="";FIN.MOIS(DATE(Année;Mois;1);0);C5))*(Nom_P=Agent!$A$3));Contact_Traité)))
ou
=SI(ESTERREUR(SOMME(SI(((DA!$A$2:$A$9999>=B5)*(DA!$A$2:$A$9999<C5)*(DA!$B$2:$B$9999=Agent!$A$3));DA!$G$2:$G$9999)));"";SOMME(SI(((DA!$A$2:$A$9999>=B5)*(DA!$A$2:$A$9999<C5)*(DA!$B$2:$B$9999=Agent!$A$3));DA!$G$2:$G$9999)))