[roriconfan]

Originally Posted by Shiosai

Ok, this is the last time I post on this,

Spoiler:

The timeline where Cell stole a time machine had a Trunks who somehow defeated the Androids. Since it's not conceivable he could defeat them without help, it's implied he had to go back at least once in time to find a weakness. So that first jump back in time where presumably he gets the blueprints is a fourth timeline. He certainly never had a chance to go back with the blueprints in the canon line.

I'm not sure there is another way to explain it without making a plothole.

Oh, you missed the part where the timeframe Cell went back to was the same as when Trucks went there the first time. He wanted to tell himself not to intervene with this timeline as the problem was solved (or he thought it was).