I've done the quest for the item but I didn't grab the item during the associated quest. I've only just now realized it was there and the antagonist is already long dead.

When I go back to the house to get the item and pick it up, it has zero vale and zero weight, but picking it up doesn't trigger an entry into the quest log.

When I take the item to Delvin, the option to sell it to him doesn't come up. I can also remove the item from my inventory unlike other items of this type.

He seems to simply refuse to acknowledge the item at all, and it's as if it's just a random item and not part of a quest at all.

Oh, and I still have a gigantic falmer eye in my shelf at home for pretty much the same reasons.

At least it's not stuck in my inventory like Gallus' Journal.