Changed plotline from story sort of ruins it (Score 1)

One change from the short story that I'm sure Heinlein would not have been happy with is making the protagonist the Fizzle Bomber. I'm not sure the movie ever explains why he was called the Fizzle Bomber, or what his motives were (I'd have to watch it again), but in the short story there was no Fizzle Bomber that they were trying to apprehend. There was a throwaway reference to a Fizzle War because the presumably nuclear bomb in New York hadn't gone off (plus a hundred other things that didn't go as planned due to interference by Temporal Agents). Now none of the Heinlein stories that deal with time travel ever involve multiple futures caused by changing something in the past, and therefore changing the future timeline (Like Ray Bradbury's 'A Sound of Thunder'). With that being the case, how did the Temporal Agency know that the Fizzle Bomber had detonated a bomb in 1975 that had killed 11,000 people, since he had been stopped before that happened? At least in the short story, history had recorded the event as the Fizzle War because it had never happened.