Imagine a string on a table and the string is taunt and thus a straight line.

Now imagine you can create a loop of that string by having being a little looser.

It is a self contained time loop for the memories were erased (and it was only months in marvel time so the age difference of the bodies were not major.) The memories were then transferred to their older selves so that something would remain of these OG 5 story wise from 2012 to 2018. Some significance happened besides the OG 5 affecting other characters in universe.

And in 2019 at the end of the 2017 and 2018 Iceman run there is a Uncanny X-Men: Winter's End #1 which is a 1 shot where Older Iceman fights Icewizard future him from Battle of the Atom shows up. Well there is a few good pages of current Bobby is talking how personal agency is removed from people if time displaced versions of you come back in time or forward in time and are trying to influence your behavior. It is not natural and it is kind of [censored] in what it is doing to people as individuals.