I think this is more a symptom of the low volume and liquidity, not necessarily Forbes's math. There are public stocks trading on the major exchanges that have

I think this is more a symptom of the low volume and liquidity, not necessarily Forbes's math. There are public stocks trading on the major exchanges that have extremely low volume, but the last trade is still the last trade and as a result they tend to fluctuate wide day-to-day. This is consistent with how the market capitalization of every company is calculated.