An agreement, even if verbal, can be a contract if the other party gave consideration (here, labor). So the story is: executive meets terms of contract with employee #1.
Oral contracts are completely binding in theory, but in practice a judge requires evidence of the contract's existence and content.
What if CEO person "yes we had an agreement, but it was for 5%, not 10%?" How would a judge decide? At best, look for written documents about the contract, or testimony from people who the CEO told about the contract.
