They have been planning this since the convoluted explanation in 2008. When the current 2010 article says, "It usually refers to people of varying ages whose lives overlap during a particular time period", it is referring to the 2008 article that created this definition (see below). Of course, this does not fit the 1st Century parallel, and no one would ever read Jesus' words and arrive at this meaning, but faith in 1914 and the urgency of the times must be maintained.
From the February 15, 2008 Watchtower; the 'box' on Can We Calculate the Length of "This Generation"?:
The word "generation" usually refers to people of various ages whose lives overlap during a particular time period or event. For example, Exodus 1:6 tells us: "Eventually Joseph died, and also all his brothers and all that generation." Joseph and his brothers varied in age, but they shared a common experience during the same time period. Included in "that generation" were some of Joseph's brothers who were born before him. Some of these outlived Joseph. (Gen. 50:24) Others of "that generation," such as Benjamin, were born after Joseph was born and may have lived on after he died.
So when the term "generation" is used with reference to people living at a particular time, the exact length of that time cannot be stated except that it does have an end and would not be excessively long. Therefore, by using the term "this generation," as recorded at Matthew 24:34, Jesus did not give his disciples a formula to enable them to determine when "the last days" would end. Rather, Jesus went on to emphasize that they would not know "that day and hour."—2 Tim. 3:1; Matt. 24:36.