That's karma. You grab at it like a bunch of greedy kids so let's knock 75 grand off the price. But really it's not even theirs. Just dumb luck and buying the right house. They could try finding the previous owner.
How the frak do you consider it "not theirs"?
He bought the crap house to tear down and use the lot, that includes everything, including all the crumpled up newspapers and crap they find shoved in the walls for insulation, it's all his, it came with the house he payed for.
Just because some of the newsprint insulation which is otherwise all garbage, turns out to valuable today, doesn't mean they can only keep the garbage.
It's for better and worse
all his now.
It's not like the comic was in a safe or even a shoebox, or actually "in" the house, like it had value recognized and to be returned in the "owner".
It was treated and used as garbage to insulate a wall, that was it's value.
And track down the previous owners? The house can have several previous owners, you don't even know if the previous owners were the ones who had it insulated with old papers and comics.
What if the comic belonged to the company who built and insulated the house, or one of it's workers, or one of it's workers kids, track him down! Or his grandam who payed for and bought it for him, do you track all them down too!
Or was bought in stock from a garbage paper recycling plant to be used as insulation, track down that "owner" ...etc
Any one of these people or their descendants can say oh yeah, that's mine because...
When the thing went into the wall like all the other newspaper, mags and rags it was considered disposable
garbage someone probably threw away. It had more value as insulation.
It wasn't in a safe for keeping, with somebodies name on it or even hidden in a place to recuperate later and accidentally "lost".
It was part of the garbage insulation which this guy payed for when he bought the house.
Rant...
