Any registration issued under the Act of March 3, 1881, or the Act of February 20, 1905, or of a mark registered on the principal register provided by this chapter and owned by a party to an action shall be admissible in evidence and shall be prima facie evidence of the validity of the registered mark and of the registration of the mark, of the registrant’s ownership of the mark, and of the registrant’s exclusive right to use the registered mark in commerce on or in connection with the goods or services specified in the registration subject to any conditions or limitations stated therein, but shall not preclude another person from proving any legal or equitable defense or defect, including those set forth in subsection (b), which might have been asserted if such mark had not been registered.