I just now realized something... (Spoiler Warning)
Man, I've seen this film a lot of times and didn't realize this small ironic detail until now.
In the first flashback scene where Norman and the Girl are outside of the office when Norman suggests going into the parlor instead of going up to his room, I came to realize something. The couple that disturbs the two that come out, the woman with the guy in the room down the way happens to be the older woman that Norman ends up killing much later.
Did anyone catch that instantly or did they realize it after multiple showings like I did?
But this one's eating my popcorn!