"Trunks's cells would've been collected..."

[Terra-jin]

Cell made this statement when he was telling Piccolo all about his origins. It implies that Trunks was there in the early days of Cell's timeline, but that throws a wrench in most timeline theories. That Trunks had to have come from yet another timeline, right?

But couldn't Cell just have referred to baby Trunks? I mean, he was actually there, only just when he was a baby. For DNA gathering purposes, this wouldn't matter, so I think it's plausible that Cell meant baby Trunks.

The anime does show Future Trunks slicing Freeza in half during this dialogue and the manga shows a panel of sliced-up Freeza, but Cell's statement itself does not specifically refer to an adult Trunks. I say he meant baby Trunks, which would resolve the plothole and allow Cell's timeline to be the original timeline.

[rereboy]

But couldn't Cell just have referred to baby Trunks? I mean, he was actually there, only just when he was a baby. For DNA gathering purposes, this wouldn't matter, so I think it's plausible that Cell meant baby Trunks.

No, the manga, while Cell is explaining things, has panels of Freeza and Cold dying just like they did when Future Trunks killed them.

In any case, I personally disregard this part as an error of the manga, just like I disregard when Trunks says to Goku that the androids are #19 and #20. Things simply make much more sense within the manga if we consider that to be a mistake, and if we don't consider it a mistake and try to make it fit it's simply an absolute mess.

It's one of those things where there is no adequate solution.

[Desassina]

Trunks' blood being collected in Cell's past is not even the problem. If we go by the manga on its own, the ending was open enough for us to know that Cell, when resurfacing from the lab that hadn't been destroyed in the future, killed Trunks by sneaking up to him and absorbing his energy (for example), took the time machine and completed the cycle. The problem is obviously DB Super returning the character, contradicting this valid interpretation, but only retroactively.

[spoiler][/spoiler]

So, what do we do, then? We don't come up with linear explanations based on cause and effect. We simply assume that there is a self correcting timeline that Trunks went back to an instance before the changes were made, which allowed him to kill the same Cell that would kill him. However, because Trunks had already been part of an alternate past, those changes won't be erased by Cell not departing. It's like Trunks' future is actually the head of a long list of past events on its tail, meaning that his time comes before the main characters' line.

This may be confusing, but when did Trunks learn about Cell killing him? In the past, ahead of his future, as if it were the other way around and he travelled forward to know what would have happened, and he did.

[LuckyCat]

I agree with OP, but well, it doesn't need to be baby Trunks. The insects that collect DNA for Cell were still operative when Piccolo confronted Imperfect Cell. We don't know when the deadline is for Cell to collect DNA, so the insects potentially could've gotten it from Trunks at any age before Cell was completed.

killed Trunks by sneaking up to him and absorbing his energy (for example), took the time machine and completed the cycle

He never says he absorbed that Trunks, and there wasn't any reason for him to do so at that time.

[emperior]

He had 20 years to complete, Trunks was born 6 months before the androids attacked if I remember correctly, so Cell had plenty of time to collect and use Trunks' cells. But as he stated, he didn't need them.