You can't say "outside of time travel episodes", because that is exactly what shows us what the past was like on this alternate universe Earth of Star Trek. Edith Keeler is a real, historical person in the Trek version of 1930. She is not a "plot intervention" internally to that universe. She's real. Just as all of the other events in every episode. You can't pick and choose which persons and events within the Trekverse are real and which are not. Internally to the Star Trek universe every ship, event, person and place are depicted as real settings and actual, historical living individuals.
