def _get_endog_name(self, yname, yname_list, all=False):
        model = self.model
        if yname is None:
            yname = model.endog_names
        if yname_list is None:
            ynames = model._ynames_map
            ynames = self._maybe_convert_ynames_int(ynames)
            # use range below to ensure sortedness
            ynames = [ynames[key] for key in range(int(model.J))]
            ynames = ['='.join([yname, name]) for name in ynames]
            if not all:
                yname_list = ynames[1:] # assumes first variable is dropped
            else:
                yname_list = ynames
        return yname, yname_list
If all is False, the first variable name is dropped
dataset/ETHPy150Open statsmodels/statsmodels/statsmodels/discrete/discrete_model.py/MultinomialResults._get_endog_name