During this episode, Sam mentions to Al how their minds got mixed up when they leaped together. He is mentioning events from the episode "The Leap Back". However in The Leap Back, when Sam's wife Donna is talking to Al, they mention that Sam doesn't remember leaping back and doesn't even remember leaping with Al at all.
In the final scene, Dr. Mason Crane is holding a Spyderco folding knife as evidenced by the round thumb hole. According to the Spyderco website, their first folding knife was introduced in 1981.
During the scene in Dr Crane's office, Al appears and tells Sam that "DiCarro isn't the killer. You are!" However, if you watch Dean carefully, he actually says "DiCarro isn't the killer. Jack is!"
After Sam wakes up from a nightmare and goes to look at himself in the mirror, a second person is also seen moving behind Sam. It cannot be Al, since his holographic image is invisible to mirrors.