During animal euthanization at the experiment's end. Did we use the anesthetic dose or an overdose?

It depends on the mode of euthanasia.  If the mode of euthanasia is a physical procedure like exsanguination or decapitation, then this can be done under a plane of anesthesia that would induce absence of the toe pinch response and there is no need to overdose.  However, sometimes the mode of euthanasia is anesthetic overdose.  Choosing one mode of over the other is usually a scientific consideration, but needs to be reviewed and approved by the IACUC.