Pensamento Judaico sobre Êxodo 28:35

Since the Torah seems specific about the sin that caused the death of Nadav and Avihu, two of Aaron's sons, it seems pertinent to ask why our sages ask so many questions about the true cause of their deaths. Rabbi Manni in Midrash Tanchuma cites four reasons, all of which are sins that carry the death penalty. A) They were drunk when they entered the sanctuary. B) They had failed to wash their hands and feet prior to entering. C) They did not wear all the priestly garments, i.e. the outer coat. D) They had not married, had not fulfilled the commandment to procreate. These reasons are very difficult to understand. In the first place, the injunction not to enter the sanctuary while under the influence of alcoholic drink, had not yet been issued. Washing of one's hands and feet prior to entering, is not even hinted at anywhere. The outer coat was a garment worn only by the High Priest, not by ordinary priests. The fact that they were both unmarried had been well known. If this indeed represented a disqualification to offering incense, why had Nadav and Avihu been designated to offer same in spite of such obvious disqualification?