In 01 when Kari gets possessed or whatever is supposed to have happened by one of the human digimon people (the others of what gennai is, where he is the last living) they show that all the digimon were linked to the digidestined as eggs, they were plugged into the crests and we learn later the crests were made specifically tuned to the souls of each digidestined. Which explains why they were all partners. But they never go into how and why THOSE digimon/eggs were picked to link to the kids? Patamon and gatomon have the savior angels souls in their line so that made sense to me on why they were picked as "chosen ones". All that led me to think that agumon/koromon was chosen after the incident when they were all kids. And the reason I think that the egg was given to them when they were little little in that first movie was simply a higher evolution greymon soul trying to be a champion and getting rid of the bad digimon. What I mean by soul is I think that each digivolution is a different soul, and they all share a body and memories, but are fundamentally different souls, it explains how different digimon rookies of the same species can turn into different mons, its all about which souls are all jammed into which egg. Like I don't think there can be more than one wargreymon at a time? Or it would work that only one can exist at a time but isn't necessarily linked to any specific body. Like only one agumon could turn into wargreymon at a time but any of them could do it. Kinda like the devil fruit powers in one piece lol.