You need to gather the contract that are the evidence of your ownership. You may own shares, in which case you should have a written contract and a stock certificate. It is possible the shares are subject to “reverse vesting” or what might be listed in the contract as a repurchase right—that basically allows the company to buy from you all or some of the shares based on certain events, such as the termination of your employment. Typically, that kind of right will lapse over time. For example,...