Bro. Splane used a vague scripture with reference to Joseph to try and explain the overlapping generation thing. It makes no sense.
Genesis 50:22,23 states: 22 Joseph stayed in Egypt, along with all his father’s family. He lived a hundred and ten years 23 and saw the third generation of Ephraim’s children. Also the children of Makir son of Manasseh were placed at birth on Joseph’s knees.
So in 110 years Joseph saw 3 generations of Ephraim's children. That roughly makes a generation 36 years long. There is nothing biblically to support an "overlapping generation".
The generation Jesus was talking to in his prophecy saw all those things occur. There is no second fulfillment. And if there is, God has a lousy way of announcing it to the earth. The Jehovah's Witnesses preaching is a monumental failure. Surely if God was backing a group to save people he would do a better job than having them stand next to carts, silently waiting for someone foolish enough to approach them.