Are there any reported historical events (ie a newspaper article written in 1965) of a person claiming to be from the future, confused about how they moved back in time? It would corroborate a story if say John Doe time slipped from 1995 and reported the incident. Meanwhile, in 1945, reports surface of an incident of meeting a strange person who was confused, distressed, oddly dressed, etc. I'm still looking for two matching stories.
That's unless a time slip is strictly crossing into "the other lane" of time, into some other time line, and ours is a "pure" line where this doesn't occur.
Or, time slips occur in the mind and not physically at all, and people, under an undiscovered set of conditions, are able to generate the "recording" of a past or future event akin to seeing ghosts, but at a higher level of detail and interaction. In this scenario, seeing future events is only possible if you set time as a non-linear factor.
Eh, I just want to dismiss the accounts as made up for attention, but the mystery is too interesting to pass up.