Thing is it absolutely isn't "easy" to tell lost versus abandoned, for the simple fact that you don't know the circumstances involved in how that disc came to be out of its owners possession. Actually, it is. Circumstances are largely irrelevant (at least in Ohio). I showed your post to my father-in-law who is a lawyer at a large firm in Ohio. His explanation was that it largely depends on whether a conscious choice was made to stop searching. In the circumstances you've listed (i.e. you know where the approximate physical location of your property) once you stop searching, regardless of reason, you have abandoned your property.
If a disc is lost late in the day, and the owner runs out of daylight in his search for the disc and leaves the course without it, is it lost or abandoned? Abandoned. He chose to leave the course. Keep a flashlight in your bag, and you won't have this issue.
If a disc is lost during a tournament round in which, by rule, the player and his group has just 3 minutes to locate it or they must move on, is it lost or abandoned? Abandoned. He CHOSE to move on. If the disc meant that much to him he could have CHOSE to forfeit and stay and look.
If a disc is lost and the player is in a rush because he's got to get off the course to pick up his kid at school, is it lost or abandoned? Abandoned. He made the right choice, kid is more important that disc, but he still made a choice to abandon that disc.
What if in the meantime, while he's picking up his kid, someone else comes along, finds his disc, and throws it into the pond 5 holes away from where it was originally lost so any attempt to return to the course and search is fruitless? Is the disc resting in the pond lost or abandoned? Abandoned by the person who found the disc after it was abandoned the first time.
In an earlier post, you said "I just don't understand if someone deems the effort to find a disc is more than the value of the disc how they think they retain ownership." My counter to that is how do you know, just by finding the disc, how much effort went into finding the disc and what the circumstances were when that effort was made? You're basing your viewpoint on an assumption. An assumption that is more likely to be incorrect than correct most of the time. The amount of effort that went into the search is legally irrelevant.
I commend you for doing the right thing with inked discs. The problem really lies with the people who make your argument about "abandoned" discs as a rationalization for keeping or attempting to profit from any disc they find, inked or not. Without being able to prove intent, it's extremely difficult to make a convincing argument that one "abandoned" a disc versus simply losing it. Nope, it's very easy to make a legal argument. Your arguments are moral. For whatever it's worth I agree with them, but they won't hold up in court.