And the Lord spoke to Moses in the wilderness of Sinai, in the first month of the second year after they had come out of the land of Egypt, saying, 2 “Let the people of Israel keep the Passover at its appointed time. 3 On the fourteenth day of this month, at twilight, you shall keep it at its appointed time; according to all its statutes and all its rules you shall keep it.” 4 So Moses told the people of Israel that they should keep the Passover. 5 And they kept the Passover in the first month, on the fourteenth day of the month, at twilight, in the wilderness of Sinai; according to all that the Lord commanded Moses, so the people of Israel did. 6 And there were certain men who were unclean through touching a dead body, so that they could not keep the Passover on that day, and they came before Moses and Aaron on that day. 7 And those men said to him, “We are unclean through touching a dead body. Why are we kept from bringing the Lord's offering at its appointed time among the people of Israel?” 8 And Moses said to them, “Wait, that I may hear what the Lord will command concerning you.”There is a time stamp given for this Passover in verse 1. We are informed that it took place "in the first month of the second year after they had come out of the land of Egypt." Thus, this was the second Passover.
In verses 6 and 7 we read of "certain men who were unclean through touching a dead body." Someone, therefore, has evidently died among the camp of Israel. Here is where it gets interesting. According to Exodus 38:26, the number of men above twenty years of age -- excluding the Levites -- who paid a tax to the Tabernacle only a short time before its erection was 603,550. According to Numbers 1:46, the number just after the erection of the Tabernacle (at the beginning of the second month of the second year) is exactly the same -- 603,550.
This suggests that the dead body that we read was touched and hence defiled certain men in Numbers 9:6-7 was likely of the tribe of Levi.
Now turn with me to Leviticus 10, in which we read an account of the very same Passover. We know that Leviticus 10 takes place around the time of Passover, since in Exodus 40 we read of the erection of the Tabernacle on the first day of the first month and that at that same time Aaron and his sons were consecrated to minister as priests (Exodus 40:13). Leviticus 8 and 9 concern the particulars of their consecration. Thus, we pick up at Leviticus 10.
In verses 1-5, we read of the death of Nadab and Abihu:
Now Nadab and Abihu, the sons of Aaron, each took his censer and put fire in it and laid incense on it and offered unauthorized fire before the Lord, which he had not commanded them. 2 And fire came out from before the Lord and consumed them, and they died before the Lord. 3 Then Moses said to Aaron, “This is what the Lord has said: ‘Among those who are near me I will be sanctified, and before all the people I will be glorified.’” And Aaron held his peace. 4 And Moses called Mishael and Elzaphan, the sons of Uzziel the uncle of Aaron, and said to them, “Come near; carry your brothers away from the front of the sanctuary and out of the camp.” 5 So they came near and carried them in their coats out of the camp, as Moses had said.No mention is made in Leviticus 10 of the defiling of certain men by touching a dead body or the instructions given as a result. No mention is made in Numbers 9 of Nadab and Abihu, of the tribe of Levi, who took a censer and offered unauthorized fire before the Lord, resulting in their deaths in judgment and their bodies being carried away out of the camp by Mishael and Elzaphan.
Thus, the "certain men" spoken of in Numbers 9 who had been defiled by touching a dead body was most likely Mishael and Elzaphan.
This sort of integration without design is the type of pattern we expect in genuine historical reports, not works of fiction.