In the book Ghosts and Haunted Places by Rosemary Ellen Guiley there is chapter called "Where Do Ghosts Come From?" A section in this lists one possibility as Time Slips. These are defined as hauntings not in our time but when someone moves back to the past and observes ghostly events. Retroconition is a term used in the field of psychical research.
One famous case is the Versailles Ghost Case:
In 1901 two English academics named Eleanor Jourdain and Annie Moberly visited Versailles Palace in France. While taking a stroll on the grounds they went to the Petite Trianon, a small house built by King Louis XV between 1762 and 1768. His successor and grandson Louis XVI gave it to his wife Marie Antoinette who loved to spend time there in the lush days prior to the French Revolution. Both Louis XVI and Marie Antoninette were beheaded during that time.
While there Eleanor Jourdain and Annie Moberly observed many people in "period costumes." dating to the Revolution. They just assumed these were staff members in costume for historical effect. But they were startled when some of them began to disapear. Both "felt weird" while they were there. At some poin the two were able to describe buildings as they appeared in the past. Their conclusion was that they had somehow traveled back to 1789 and while there had actually seen Marie Antionette herself in the Petite Trianon's garden.
Other reports of similar experiences have come out of Versailles. Psychical researchers have studdied the reports but no satisfactory explanation can be put forth to either support or disprove the time slip explanation.