Continuity mistake: When Shelly Duvall is crying, backing up the stairs and swinging a bat at Jack Nicholson, the positions of both of their arms and the bat change dramatically as the camera shots switch back and forth between them.
Continuity mistake: As Jack talks and yells to Wendy at the writing spot, a chair appears behind him between shots.
Continuity mistake: Wendy is smoking a cigarette when Danny starts screaming, then she runs into the bedroom and opens the door, and doesn't have the cigarette.
Continuity mistake: In the scene at the beginning of the film, when Doc and Mr. Hallorann are eating ice cream, if you pay attention to Danny's hands, they move from folded in front of the ice cream bowl, to the back, and so on. They move about 5 times, each different.
Answer: Delbert Grady has always been at the hotel, just as Jack Torrance has...however, "Charles Grady" was one incarnation of the hotel's "caretaker", which Jack Torrance currently is. Delbert, evidenced by his appearance, occupation, and archaic racial views, has been with the hotel since its turn-of-the-century inception, just as Jack, in the photo at the end, has been. We don't know what "spirit-Jack's" function in the Overlook is...we only know that the present Jack (whom Delbert is talking to) embodies the "caretaker" who has always been there, just as Charles Grady did in his time. Delbert refers to his wife and two daughters, whom he did not murder...his "caretaker" version, Charles Grady, did that.