You're absolutely right and wrong. Any shares can be sold if there is a buyer. Preferred shares can be sold to sophisticated investors and not registered. Restricted common shares can be sold the same way. HOWEVER, neither restricted common NOR preferred shares can enter the public market unless and until their restrictive holding period of six months has passed. Additionally, in the case of TPAC there must be a sufficient number of authorized common shares available in order to convert the preferred into common. Simple math shows that TPAC doesn't have adequate common to cover all of the preferred. So there is an additional layer of protection against dilution.