Section 6A. No instrument conveying unregistered land shall be accepted for recording unless (a) the instrument indicates that the land conveyed is the same as described in or conveyed by prior recorded instruments identified sufficiently to locate the place of recording within the registry, or states that the instrument does not create any new boundaries, or (b) the instrument identifies the land conveyed either by reference to a plan or plans previously recorded in the same registry of deeds and identified sufficiently to locate the place of recording therein, or by reference to a plan or plans recorded with the conveyance. Failure to comply with this section shall not affect the validity of any instrument.