As far as Rey Mysterio's contractual status with WWE is concerned, his deal reportedly expired last week. From there, Vince McMahon renewed it for one year, despite not having such an option to do so in the contract. WWE contracts are allowed to be frozen in the event of an injury to a Superstar.
WWE went with the mindset that since Mysterio missed so much time during his contract period due to various injuries, that he owed them the time and he was renewed through May of 2015 on that basis.
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(Partial Credit: Wrestling Observer Newsletter)