I think that because Aaron was acting under Moses’ instruction and on his behalf, the words of God that Aaron said and the miracles God Did using Aaron’s staff and his words, were Often attributed to Moses - in the records as it were. Just as we sometimes would say the word of God says... or God says... when quoting any prophet or apostles written words In the bible because they spoke (As per His instruction) on His behalf. Below are some of the portions of scripture that lead me to this conclusion.
Acts 7
36 He (Moses) brought them out, after that he had shewed wonders and signs in the land of Egypt, and in the Red sea, and in the wilderness forty years. (All Credit went to Moses in Stephens speech despite the following verses often crediting both men or Aaron as acting or speaking)
Gen 4
16 And he (Aaron) shall be thy spokesman unto the people: and he shall be, even he shall be to thee instead of a mouth, and thou (Moses) shalt be to him instead of God.
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29 And Moses and Aaron went and gathered together all the elders of the children of Israel:
30 And Aaron spake all the words which the Lord had spoken unto Moses, and did the signs in the sight of the people.
Exodus 7 and 8
And the Lord said unto Moses, See, I have made thee a god to Pharaoh: and Aaron thy brother shall be thy prophet.
Thou shalt speak all that I command thee: and Aaron thy brother shall speak unto Pharaoh, that he send the children of Israel out of his land
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thou shalt say unto Aaron, Take thy rod, and cast it before Pharaoh, and it shall become a serpent
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Say unto Aaron, Take thy rod, and stretch out thine hand upon the waters of Egypt, upon their streams, upon their rivers, and upon their ponds, and upon all their pools of water, that they may become blood.
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Say unto Aaron, Stretch forth thine hand with thy rod over the streams, over the rivers, and over the ponds, and cause frogs to come up
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Say unto Aaron, Stretch out thy rod, and smite the dust of the land, that it may become lice
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Exodus 9
3 And Moses and Aaron came in unto Pharaoh, and said unto him, Thus saith the Lord God of the Hebrews, How long wilt thou refuse to humble thyself before me? let my people go, that they may serve me.
Exodus 11
10 And Moses and Aaron did all these wonders before Pharaoh:
Exodus 14
43 And the Lord said unto Moses and Aaron, This is the ordinance of the passover: There shall no stranger eat thereof: