the idea that a person can claim a line indefinitely seems misguided at best, and it seems as though you suggest that honoring such a claim is the only polite way to proceed.
I am saying that it's quite the opposite, and a decent case can be made that to claim ANY line as one's own reeks of impoliteness. Artists of Japanese tradition would not even sign their paintings because to do so would be an obvious reference to self, ie ego (ego transcendence is what they were after, although certainly not the case with most climbers today).
So to me, claiming rights to a piece of publically owned rock is nothing but ego aggrandisement, and it needs to be understood as what it is. It's a need to be first, a need to be recognized, a need to leave a territorial piss mark upon the landscape of the climbing community. Whether or not you think this an acceptable form of behaviour is irrelevant really (since i concede a 6 month window for one to leave this stain), but let's at least call it what it is.
You keep saying this, and we have all agreed. Do you have anything else to add?