I think you're being too anal about this.
Is this a backdoor way of suggesting the Guardian isn't all he's cracked up to be?
If so, it must be a full Moon.
I'm just wondering why the Guardian didn't let them just bring her to the future. It removes her from history but keeps her alive.
Butt would she have dumped Kirk like Gillian Taylor did?
There is no Edith-McCoy only time-line.
Actually the novel Crucible: McCoy - Provenance of Shadows explores the possibility of such a timeline.
Powerful scene when McCoy finally sees the tricorder readings from the alternate history where he is trapped back in time.