Archive footage

Archive footage is the term given to footage from stories that ends up being reused in later stories. It's used as a flashback or to make a character seem there. The process is more common in the revival of Doctor Who but this has occurred in the "classic" stories Logopolis and the beginning of The Five Doctors.

The process was originally to be used in Dimensions in Time, but this fell through.

The process has been used not as a flashback but to incorporate characters within a story. The Name of the Doctor uses this so it seems the Doctors are there in the story.