No award of compensation shall be rescinded, altered, or amended after five years from the date of the injury except upon a petition by a party in interest filed within such five years and any counterpetition seeking other relief filed by the adverse party within 30 days of the original petition raising issues in addition to those raised by such original petition. Provided, however, that after an award has been made finding that there was employment and the time to petition for a rehearing or reconsideration or review has expired or such petition if made has been determined, the appeals board upon a petition to reopen shall not have the power to find that there was no employment.
Ca. Lab. Code § 5804