I actually noticed that too. The montage from episode 5 had lots of those sneak previews, thanks for mentioning some of them here, @ForeverFanatic.
All of those scenes in the order they came up in the montage are as follow:
**The one from episode 8 when Do Hyun Su returns home and Cha Ji Won is waiting at the door and they have some bittersweet talk together.
**Episode 9 begins with a flashback to the time they got a new home and Do Hyun So had a suprise house warming party ready, it also hinted that "the scene when he tells Ji Won it's okay to open her eyes now"
**Episode 10, Do Hyun So running towards Cha Ji Won and pointing towards the watch on his hand "It's still a few minutes before 1 hour passed"
**Back to Episode 8 again, Cha Ji Won getting rid of evidence, hence burning even the recorder and Do Hyun Su's bag.
**The one Pro57 mentioned, Episode 11, Ji Won telling him to go some where no one could find him, not even herself.
**Episode 8, Ji Won overhearing the conversation between the siblings and leaving the scene, the latter scene is shown in the sneak previewing.
**Last in the sneak preview, is Episode 11, when we got the emotional hit. Do Hyun Su came back home and looked at the pictures of them three as family and crying out his heart (probably realizing how precious (not important) they are and he is so hurt from almost losing it!
I just want to say wow! Such a strong and beautiful MV that montage was, even from episode 5, all those scenes were hinted yet it was as unpredictable as ever, and it was crafted just so perfect! I was really hoping we will get some other episode ending with that kind of montage, this time hinting at the last episode! And episode 11 was the most likely, but it didn't happen yet. so I don't have an idea what's coming!