My assertion is that there is no such thing as temporal duplicates if there is only a single immutable timeline.
You from ten minutes ago is you from now.
(But that's not how Star Trek works.)
A great 20th century philosopher once said "I yam what I yam" which just about covers all my thoughts on the subject completely, and yet I continue...
They are connected, your future old self will not survive the death of his junior if we believe in the one set of rules above another for some arbitrary reason, but even if you factor in divergency and paradoxpfoofness you might as well...
Does it really matter where the timeline branches?
If two yous have a year each of individual history (because of a fork in time) you do not share, are you still the same person? Obviously not, but you're still people full lives behind you and in front of you, although in the Charmed universe, temporal dopplegangers eventually collapse into each other and the memories of their adventures conflate with their bodies, which is probably similar to the crazy shit that happened to Ashton Kutcher's brain in the Butterfly Effect, 20 new years of engrams digging their way through his gray matter right on top of everything thing else he's already got in a few seconds.
The word "duplication" has connotations.
To me at least it implies original vs. copy/copies.
There are after all only 6 real Mona Lisa's in the world, even if they all have "this is a fake" written in sharpee under the first layer of oils any fool with an X-Ray can see.
So yeah, in Star Trek, I BELIEVE (which is not necessarily the truth) that temporal duplicates are real persons who are all still the originals of themselves, who are not copies or dupicates. No one was duplicated, they all got pulled out of their mothers or what ever happens when real men are off playing golf, and lived an exemplary life of an individual no matter how many times that life has been closely mirrored across an infinite amount of Universes.