If you read the legal documents, instead of Sam's attempt to try the case in the media, you'll see it's quite clear. There are signed documents stating Guillory owned half the equity. These documents were in YC's possession. Nothing ever voided them.
Instead of separating Guillory early and cleanly, they dropped the ball, and attempted to shame him, attempted to threaten him (Sam called Guillory dozens of times in a single weekend and told him to take a small buyout or he'd never work again), and then only as a final result did the thing they should've done out of the gate: negotiate a settlement.
Instead of separating Guillory early and cleanly, they dropped the ball, and attempted to shame him, attempted to threaten him (Sam called Guillory dozens of times in a single weekend and told him to take a small buyout or he'd never work again), and then only as a final result did the thing they should've done out of the gate: negotiate a settlement.