What about before birth and after death? According to the popular view, individual souls migrate here from another realm, let's call it Zoop, and when the body dies, return to Zoop, sometimes never returning to Earth, but enduring to eternity. Some may think of this eternity as just more time, time filled with very different kinds of experiences perhaps, but still abiding, one-way, flowing time. But in the realm of the spirit there is no time. So in a certain sense it is not true that the soul was formed before the body and will endure after the dissolution of the body, because technically there is no before and after except in Earthly, embodied life.
For those who ascribe to the popular view, and ascribe to some theory of reincarnation, the process would look something like this: Dorp is born in 1900 and lives until 2000. Then he dies, and his soul goes back to Zoop for some non-zero period of time, during which it is determined that this soul must go back to Earth. So the earliest time the soul can come back for a new life is in 2000, the moment after Dorp dies. Of course, the waiting period could be longer. Perhaps he won’t come back until 2050 or 2500.
But if there truly is no time in the spirit-realm then there is no reason why a person can’t be reincarnated at what on Earth would be considered earlier than the time of death. The question is, what if “after” death, Dorp’s soul is reincarnated in 1940 and lives to 2040? In that case, the same soul can be wholly present in two individuals living on Earth at the same time!
If so, then you might have met yourself in another person already. Literally.
Perhaps there is only one soul.
I'd also mention in passing that in the Indian notion of reincarnation, there is no Zoop.
More to come on this topic)