That Jesus or Paul or the editors of the Genesis narrative (Elohist and Yahwist) may have believed that Adam existed is no proof that Adam actually existed in time and space history.
Assuming that fundamentalist Christians are correct and that Adam was created 4000 CE, then the "proof" they offer up for his existence is all hearsay written at least 3000 years after Adam's supposed creation, Genesis 2 ( written 960 BCE - Elohist editor) and as late as 4000 years after his supposed creation, I Timothy ( written 100 - 150 CE - a forgery).
Thus the oral tradition about Adam must have survived 3000 to 4000 years completely unchanged to when the bible stories were written ...... and pigs might fly.
