One favorite trope I always love to think about is delivery of a letter from the past to a point of accidental (and one-way) time travel.
There are two people (A & B) at present (can be generalized to a group of people).
B got accidentally transported to the past (same timeline).
At present, B is already dead after living his/her full life, but he/she dispatched a letter to A at precise date, time and place of his/her disappearance.
At present, A gets letter from B just after B's disappearance.
There are two examples of this trope in my mind at this time:
In the end of the Back to the Future 2 (1989) movie, Doc got transported to the past because of an accidental lightning strike on his time machine. Moments later, Marty got 70 years old letter from Doc.
In the Doctor Who (2005) episode Blink (2007), Sally's friend got transported back to the past by a Weeping Angel and moments later Sally got a letter from her disappeared friend in which she explained where she ended up and how she seduced a man.
Which Sci-Fi work introduce this idea?