Exodus 9 Then the Lord said to Moses, “Go to Pharaoh and say to him, ‘This is what the Lord , the God of the Hebrews, says: “Let my people go, so that they may worship me.” 2 If you refuse to let them go and continue to hold them back, 3 the hand of the Lord will bring a terrible plague on your livestock in the field—on your horses, donkeys and camels and on your cattle, sheep and goats. 4 But the Lord will make a distinction between the livestock of Israel and that of Egypt, so that no animal belonging to the Israelites will die.’ ”
5 The Lord set a time and said, “Tomorrow the Lord will do this in the land.” 6 And the next day the Lord did it: All the livestock of the Egyptians died, but not one animal belonging to the Israelites died. 7 Pharaoh investigated and found that not even one of the animals of the Israelites had died. Yet his heart was unyielding and he would not let the people go.
Notice all of the Egyptian cattle have been killed
Exodus 12:29 At midnight the LORD struck down all the firstborn in Egypt, from the firstborn of Pharaoh, who sat on the throne, to the firstborn of the prisoner, who was in the dungeon, and the firstborn of all the livestock as well.
See where this is going? If YHWH had just killed all the cattle in a previous plauge, how were there any firstborns of the cattle left to kill? Impossible if this is a true account but possible if it is an oversight of a bad storyteller centuries later. Any WT explanation for this?