I'm sure there aren't exactly millennia of reports. I actually wrote an article in which I talked about reported OBEs a little. But these hardly count as solid evidence.
Scientists actually tried to prove or disprove the accuracy of OBEs, by placing hidden signs in operating rooms where dying patients claimed to have floated around during resuscitation. If their claims were true, their "souls" would have been able to notice the signs which were not visible from a standing position.
Unfortunately, none could accurately describe these hidden signs, because their OBE was not a real physical appearance, but merely something that happened inside their brains.
Psychedelics, like drug trips, also only happen in our brain by changing the chemical compounds and influence the neuronal transmissions.
It's like having your TV flicker in crazy colors because a dust particle causes an electric discharge somewhere in its transistors.
The current understanding of OBEs is that our brain tries to protect itself from harm while it's dying, so it's trying to create a pleasant experience.
Another factor that speaks in favor of this theory is that OBEs show cultural and geographical influences. Christians see angels or god. Non-religious people don't see any angels or gods.
If "the beyond" was real, it would most likely look the same for us all and not be dependent on what we saw and learned in our personal lives.