Every duly recorded satisfaction piece or instrument executed prior to January 1, 1980, with intent to cancel and discharge or assign a mortgage of real estate, fully identifying the mortgage so intended to be canceled and discharged or assigned, but not drawn in formal accordance with statutory requirements, shall be held a valid discharge or assignment of such mortgage and a release or assignment of the mortgaged interest in such real estate. This section shall not apply to such satisfaction pieces or instruments, the validity of which is brought into question in any suit pending in any court before January 1, 1987.