When considering Electre's valued outranking relations, aggregation/disaggregation methodologies have difficulties in taking discordance (veto) into account. We present a partial inference procedure to compute the value of the veto-related parameters that best restore a set of outranking statements, provided by a decision maker ( i.e., examples that an Electre model should restore). This paper complements previous work on the inference of other preference-related parameters (weights, cutting level, category limits, ...), advancing toward an integrated approach to inference problems in Electre III and Tri methods. We propose mathematical programs to infer veto-related parameters, first considering only one criterion, then all criteria simultaneously, using the original version of Electre outranking relation and two variants. Depending on the case, these inference procedures lead to linear programming, 0-1 linear programming, or separable programming problems. The partial inference programs are considered as problems to be solved several times in an interactive process, where decision makers continuously revise the information they provide as they learn from the results.