The law doesn't work like that.
It's exceedingly strange to have had the initial cofounder depart and nothing was done to formalise the terms of that separation.
Also Sam seems really annoyed that this ghost-co-founder has turned up with this claim at the most inopportune time, and suggests that this is bad behaviour. I don't think so, it's the right way to play it. Wait until you have maximium leverage and then play your legal cards. The missing cofounder would have been a fool to play it any other way, thereby losing his leverage. The evidence that he has played it right is that so many people are running in circles desperate to resolve it - he has them against a barrel.
It appears the due diligence was pretty loose. Heads will roll.....