At the end of the day, since this is using multiple worlds. Say you travel to the past, what it actually means is that you travel to what matches your interpretation of the past which is a pointless venture since you have chosen to observe what agrees with your viewpoint.
Yes, you cannot be 100% sure of it, hence why I may argue it is the result of memory and knowledge, there's no concrete past that one may know of. Devil's Proof, this "true past" may as well be God, or the aether with no way to prove it nor any method to disprove it. Unfair, I admit but it nonetheless sustains the matter.
Not only is it unfair, it is meaningless. The exact same argument that you use to say that travel to the past is impossible, I can use to say that travel to my house is impossible. Since travel to my house is possible, your argument is invalid. Your conclusion is valid with your assumptions, but the conclusion is inconsistent with reality and is therefore untrue.
It seems that I have made a second mistake:
traveling to the past and changing it is impossible. Yuri reconstructed the past so I suppose you could say that she pseudo-time traveled and bypass any argument of mine against. Hence I suppose it is better to say one can time travel, what one cannot do is change the past. Think of a computer, it performs reversible actions, you may even say it is deterministic in function. You may perform something and reverse the process before doing something else. That does not mean the undone process did not occur, you merely made it seem like the past was changed. Go back to the multiple worlds thought experiment, you travel to that past and you change it, but it is not the original world, it is not the past of the original world but rather one identical to its past. Hence, in either case presented, traveling to the real past does not occur nor would changing it change the past.
Indeed, Emp seems to be fond of such things. But honestly, emp, it's bigger than most of the people it's stabbing. xD
Just in case they somehow survive the stabbing, they'll have to deal with it in a few years