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.
That is possible. Many coins that were thought of being "lost" have already resurfaced.
Just a few weeks ago someone signed a message with 100 addresses each containing 50BTC.
I was surprised that the bitcoin market did not react to it in any way. That was 5000BTC that were thought lost until that moment.