Probably lost coins refer to so-called "zombie coins". Zombie coins are coins that have been inactive since the launch of the first BTC exchange in July 2010. Zombie coins are probably lost, as there is a non-zero probability that they can still be spent. Note that over time the chart steadily decreases as coins from before July 2010 are spent, eventually converging to the real number of lost coins. "Patoshi" coins are included in this category.

This is the Point-in-Time (PiT) variant of Probably Lost Supply. PiT metrics are strictly append-only and their history is immutable. The historic data does not necessarily reflect the best current knowledge, but the information at the time when a data point was first computed. PiT metrics are ideal candidates for applications in model backtesting and related quantitative purposes. Read our article on PiT metrics for more information.