The certificate of the prothonotary of any court of this commonwealth to an acknowledgment of a sheriff's deed, heretofore made, although not under seal of office, shall be sufficient evidence of such acknowledgment, notwithstanding no other record was made thereof at the time of such acknowledgment: Provided, That the provisions of this section shall not be construed to affect any bona fide holder or purchaser, who had neither actual or constructive notice of the execution of such sheriff's deed.