Jesus said "this generation". It clearly means, his first century contemporaries. For instance, let's read the following verse:
"You unbelieving and perverse generation," Jesus replied, "how long shall I stay with you? How long shall I put up with you?....(Matthew 17:17)
Here we also clearly understand what Jesus meant by "generation", but Witnesses want to read
"You unbelieving and perverse overlapped Fred Franz generation , how long shall I stay with you?"