Revealing mistake: In the first scene, when Nicholson is driving to the Overlook, the shadow of a helicopter can be seen at the bottom right. This is only visible in the un-matted VHS print and fullscreen DVD. (00:01:05)
Revealing mistake: Wendy has a baseball bat in her hand and Jack is trying to get the baseball bat. When Wendy hits him over the head, the baseball bat bends.
Revealing mistake: In the shot just before when Jack finishes axing the bathroom door, one of the broken pieces of wood is resting against the camera.
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.