OOMPA
What you fail to understand and appreciate is the simple fact that the entire Olivet Discourse is a exegetical nightmare for scholars and theologians and so there are sound reasons why FDS has had to revise its understanding of matters including that much vexed phrase 'this generation' in Matthew 24:34. The only thorough academic study on this phrase in English that I have sighted is by Ernest Lovestam published as a Monograph in a Series edited by J. Lambrecht, 1980, republished in 1995 under the title Jesus and 'this Generation'.
So there is a paucity of exegesis on this phrase but abundant exegesis of the entire Olivet narrative all with much confusion with past and present scholarship. Therefore, by paying close attention to the text, its context and with Holy Spirit we how have certainty of interpretation and all of us can be ever so grateful and humble. May the Lord be praised!
scholar JW