(d) If licensure or proper licensure is controverted, then proof of licensure pursuant to this section shall be made by production of a verified certificate of licensure from the Contractors State License Board which establishes that the individual or entity bringing the action was duly licensed in the proper classification of contractors at all times during the performance of any act or contract covered by the action. Nothing in this subdivision shall require any person or entity controverting licensure or proper licensure to produce a verified certificate. When licensure or proper licensure is controverted, the burden of proof to establish licensure or proper licensure shall be on the licensee.