I'm learning all the time. I'm coming to conclude that the 'Memoires of the Apostles' Justin refers to, to be an early harmonization, not a fragmentary collection as B. Ehrman holds. Interestingly leolaia 20 years ago mentioned as much in a thread. It illustrates the popularity of the idea of a singular harmonization very early. His student Tatian of course famously produced the Diatessaron that served as the Gospel for the Syrian Church for hundreds of years. How much he followed the 'memoires' is unknown. This complicates the idea that the Mark,Matt,Luke order for my hypothesis regarding an addition to Mark 13. It would seem either Justin simply forgot the Jesuine prophecy, it was not included in the Memoirs, or the addition was added individually to the 3 in an increasing expansion. That last option seems very unlikely.****
So, I have to suggest either Justin somehow simply forgot the prophecy, or it was not in his 'harmonization' for some reason that I can't imagine. I still believe the prediction of the fall of the Temple and Jerusalem are secondary to the flow in Mark. As it creates awkward reading and has confused readers for 1900 years. The writers of Matt and Luke simply followed suit, adding their own touches.
****This also assumes the present form of Justin's works is original and the quotations/paraphrases of the Gospels are original.