To be honest, with regard to the number of lost bitcoins, no one can be sure, it can really be lost or it can appear suddenly.
Debates like this will make us tired and useless to debate.
That's possible, chances that those so called lost btc are just secretly holds by certain individuals or groups and just appear
inside the market one day.
I think it's better if we focus on collecting bitcoin, after all, what
circulates 18 million is true or not. That has no effect on the price of bitcoin right now, we shouldn't think too much regarding
market cap. Bitcoin promotion and adoption are the most important for now.
Though the arguments in terms of actual numbers of existing coins will possibly increase it's value from the market it's
still best to think of investing more and try to accumulate and hold.