Remember in the Blendin Blandin eps there's time-travel-tomfoolery? WHAT IF THROUGH TIME TRAVEL PEOPLE CAN ACCIDENTALLY MEET THEIR (P)REINCARNATIONS??????????????????????
Just remember certain things:
1) Only certain people in a certain era have regular access to time travel tools. If the character is not a member of Time Baby’s anomaly repair squads or other time cops, then a time machine might be very, very difficult to get hold of.
2) People don’t remember their preincarnations. Generally, they don’t know anything about their preincarnations at all. Testing can be done to give them an idea of their last incarnation at least according to RB, but this isn’t typical knowledge. Honestly, an anomaly squad member could meet a preincarnation and never know it.
3) No paradoxes. No revealing the future in such a way that the future would change for it. No altering past events. No foreknowledge which the past character never had. Any of these things will bring the anomaly squads down on the perpetrator. They can track these and they will find out and then fix it.
4) The sheer number of people in the world at any given time means that the odds of just so happening to stumble across this particular one are astronomical.
So as far as canon goes...this probably wouldn’t be a common thing. Technically possible, yes, but very, very unlikely.