I'm a little confused as to how this works; are you saying that he manages to go back in time but when he gets there there is now a whole lot of people who were never there before?
Surely the only person who would realise would be the time traveller himself, and if we are talking about an alternate history type thing, then everything and everyone would be completely different? The collective name would be everyone.
If you are saying that it is mainly the same but there are also a whole lot of new people are introduced, then again who would notice at all? How would even the time traveller know unless he knew absolutely every person in the world?
The People who become aware; how does this happen? Does he tell them? do they believe him?
I am terribly sorry if I am coming over as negative as that is not what I'm intending, I'm just trying to understand a bit better. There just has to be a way that these people are different. Here lies the key to your question, I believe.
Maybe these new people have a particular personality trait that is what marks them out as the neverborn (that was meant to be never were but I thought it was cool so left it in!) or something. Maybe they have no belly button because they never needed one. I think your collective name should be based on something like an observation about their appearance or behaviour patterns rather than an greko-latin posh-sounding name that someone in the story is going to have to either explain or think something along the lines of 'I've got a cool name for them folk who shouldn't be here....'. That way it will be more instinctive a label and a more believable in my opinion.
If it is a blip or schism in the time-space continuum thingy-bob (I won't pretend to understand that stuff!), then maybe they are all completely identical like a glitch on a computer game or something - this would lead to all kinds of conflict and confusion that would add a real spin to the story. They could even all be John Doe-s because they have no past or identity (then it would make sense to call them the JohnDoes).
I am also in agreement with I,Brian. My WiP was full of name places like <big-human-city> and people like <Sam's-friend-from-school> until inspiration struck, then I went back and replaced them all. I'm actually still waiting for a name for <Orion's-house-in-the-woods> and my WiP is finished!
Food for thought, and again, I apologise if I have come over the wrong way, but at least I have managed to provide you with such gems as: everyone, neverborn, bellybuttonless, same-ies, JohnDoes and <others>.
Oh dear, maybe you should just ignore me lol!