but how can you tell if a bitcoin has been lost, i.e. the PW is lost or wallet file destroyed, or if it is being horded, i.e. tucked away for a rainy day?
There is no mechanism that allows you to prove that the private key has been lost forever.
Some day in the distant future, you can probably guarantee the private key will be recovered; if it is still valuable.Because, eventually, technological advances, will allow the RSA algorithm to be defeated, and then the old private keys can be cracked ----- if cracking the older key can generate sufficient value to offset the cost of cracking it, then someone other than the owner will probably crack the asymmetric key, and recover the bitcoins; 100 years from now or so.
it would seem wrong to artificially expand new bit coins in the future because some are being saved now.
Difficult, yes, since so many stakeholders would have to agree to the change -- or else the network would face a divergence of the blockchain.
But what do you mean here by "wrong" ?
If someone is "saving" Bitcoins, say, without transacting ---- there is no promise to these people that everything about BTC will continue perpetually into the future, functioning exactly the way it does today, with no protocol updates or other changes. That would be a totally unrealistic expectation: and all participants are (or should be) aware, that potential changes to the protocol have the potential to create new risks --- your BTCs in BTC terms may be safer than most fiat currencies, but don't delude yourself into thinking Bitcoin itself isn't fiat, or delude yourself into thinking there are no economic risks.
If circumstances arise, that cause the miners to collectively agree that increasing the total amount that will ever be awarded is the expedient solution, then Bitcoin will evolve that way.