Based on my related experience I don’t think most people would care where the corpse comes from thus would not require a killmail as proof of anything, if they want to buy the corpse they do so as long as it is legit and not just an alt renamed to seem the same or a totally different one.
Not entirely sure about contracts but it is guaranteed you can see the names of the corpses if you open a direct trade window and put them there, at least the last time I sold corpses where the buyer wanted to check their names used this method and worked. The good thing is you can drag and drop corpses en masse so even if you have a container full (1,000) you can do it then the buyer can cherry pick the ones they want.
But it all depends on for what reason one buys them (see my related blog article) and never had anyone care about how the corpse was acquired even when they bought them as collector’s item.
Corpses stay on space for a long time, it is helpful for gate camps, other than that it’s boring. CCP failed when they made corpses with no relation to kill reports.
The superior PVP game, Ultima Online, has a skill called Forensic Evaluation and you can find out about the kill when you find a corpse. On EVE we can investigate by clicking the wreck, then pulling the name of the owner, then spying on zkillboard or finding the body and looking up on zkillboard… and many times zkillboard has nothing to say about it.
So bodies on EVE are meh. If we had the Captain’s Quarter and if could build a throne of skulls than it would make sense hoarding corpses… or if you could swear allegiance to Blood Raiders and steal some free skill points from the corpse… etc.
A throne of skulls which you could click and see list of names of all those skulls then it would be amazing. But the people from that place where CCP is have no sense of humor apparently, they only sold us grind, clicking, boring tasks.
They way, we gankers think, if someone is trying to sell our corpses (because our corpse is rare to get - we are that good escaping) wewill mass suicide to generate tons of our corpses and sell them ourselves just to ruin such bussiness.
I did have many chances to collect my own many times but I wouldn’t want to cheat as I was on other pilots at the time and it would not be fair so I ask did you cheat that kill mail or did you use your main?