John Lightfoot on Luke 10:1

[Seventy.] Why the Vulgar should have seventy-and-two, they themselves, I suppose, are able to give no very good reason: much less the interpreter of Titus Bostrensis, when in the Greek copy before him he saw only seventy, why he should render it seventy-two.

Aben Ezra upon the story of Eldad and Medad hath this passage: "The wise men say, That Moses took six out of every tribe, and the whole number amounted to seventy-and-two: but whereas the Lord had commanded only seventy, the odd two were laid aside." Now if God laid aside two of those who had been enrolled, and endowed with the Holy Spirit, that so there might be the just number of seventy only, we can hardly imagine why our Saviour should add two, to make it seventy-two and not seventy. "It was said to Moses at Mount Sinai, Go up, thou and Aaron, and Nadab and Abihu, and seventy of the elders of Israel: so will the holy blessed God ordain to himself in the world to come a council of elders of his own people." Now the number of this consistory, the doctors determine to be no other than seventy. A council of seventy-two was never heard of amongst the Jews, but once only at Jabneh.

"R. Simeon Ben Azzai saith, I received it from the mouths of the seventy-two elders, on the day when they made R. Eliezer Ben Azariah one of the Sanhedrim." Nor did they then remove Rabban Gamaliel, although he had displeased them.