As per Daizenshuu:
Timeline 1: Main Timeline
Timeline 2: Trunks' Timeline
Timeline 3: Cell's Timeline
Timeline 4: Unseen Timeline
So, because of Trunks' Time Machine, 3 additional timelines where created. But Super introduces a few new things:
- There are 4 green Time Rings, meaning that in total, 5 different timelines exist.
- Trunks' Time Machine created only one additional timeline instead of three, and the other timelines existed since before that.
- Trunks' Time Machine can travel between timelines without creating new ones.
Timeline 1a: Original Main Timeline/Black's Timeline
Timeline 1b: New Main Timeline
Timeline 2: Trunks' Timeline
Timeline 3: Cell's Timeline
Timeline 4: Unseen Timeline
In Black's timeline, Future Trunks never returned after the Cell Games, and Zamasu became Goku Black & left to Future Trunks' timeline. His attacks cause Trunks to flee back to the main timeline, but before Zamasu became Black. This erased Black's timeline, and replaced it with a new timeline where Trunks returned, and Zamasu got killed before he could become Black. Or rather, the timeline that Black came from was "altered" instead of having a new timeline.
So, my theory is this (and I'm gonna renumber the timelines):
Timeline 1a: Cell's Timeline
Timeline 1b: Trunks' Timeline
Timeline 2a: Unseen Timeline
Timeline 2b: Original Main Timeline/Black's Timeline
Timeline 2c: New Main Timeline
Timeline 3: Unseen Timeline
Timeline 4: Unseen Timeline
Timeline 5: Unseen Timeline
Trunks (from Timeline 1a) went back to the past and killed Freeza, which created a new timeline (Timeline 2a). He returned to his timeline, and then went back to the other timeline & deactivated the #17 & #18. Then he returned to his future, but as he was about to go back to the past again, Cell killed him and went 1 year back before Trunks' first trip, altering Timeline 2a, making it Timeline 2b. Like before, Trunks comes back & forth from Timeline 1a to the past, but this time he comes to Timeline 2b, and has different experiencies thanks to Cell's appearance. So, when he returns to his world, it gets altered, and becomes Timeline 1b, where instead of getting killed from Cell, he kills Cell. Then years later in Timeline 2b, Zamasu becomes Black and goes to Timeline 1b with his Time Ring, which causes Trunks to go back in time but before Zamasu became Black, altering Timeline 2b into Timeline 2c, where Zamasu gets killed instead of becoming Black.
So basically, like the timeline where Goku & his family get killed by Zamasu/Black doesn't exist anymore, the timeline that Cell killed Trunks & the past timeline that Trunks from Cell's timeline went to, also don't exist anymore, which is why no additional green Time Rings were created. Which also means that Trunks' theory was wrong, and he can alter history with his Time Machine, instead of making new timelines.
I hope this made sense.







