The problem with the original Sin Cara (Mistico) at the Juan de la Barrera Gym show last week is that WWE doesn't want him to appear on TV for another promotion due to his 90 day non-compete clause. WWE doesn't care if he works independent shows, but he can't appear on TV until the clause expires.
Mistico claims that after May he will be able to use the Sin Cara name on TV. He says his lawyers are still working on it as part of his deal. WWE is currently using the name and own the intellectual property rights to it. Obviously, this is going to create issues and a lawsuit is likely coming.
We'll keep you posted as we hear more.