Sec.   15.   Incomplete   instrument   not   delivered.   -   Where   an incomplete  instrument  has  not  been  delivered,  it  will  not,  if completed and negotiated without authority, be a valid contract in the  hands  of  any  holder,  as  against  any  person  whose  signature was placed thereon before delivery.
 

APPLICATION OF PROVISION

      Section applies to an incomplete and undelivered instrument
 

INSTRUMENT NOT VALID AGAINST PARTY BEFORE DELIVERY

      Situation: A signs a blank check, which was subsequently stolen by B and  fills  up  the  amount  and  a  fictitious  name  as  payee.    He  then indorses the same to C, C to D, D to E, and E to F.  Can F enforce the instrument against A?   
      The answer is NO, because against A, whose signature was placed on the check prior to delivery, the instrument is not valid.
      The  answer  would  still  be  the  same  in  case  F  was  a  holder  in  due course.  Why?  The law doesn’t discriminate on what kind of holder.
      However,  the  invalidity  of  the  instrument  is  only  with  reference  to parties whose signature appears in the same prior to delivery.  As to parties whose signature appears after delivery, it may be valid.
 

IT IS A REAL DEFENSE

      The  possible  defense  of  a  party  whose  signature  appears  on  an instrument prior to delivery is that, as against him, the instrument is not valid for having been incomplete and undelivered
      Want  of  delivery  of  a  mechanically  incomplete  instrument—defense that cannot only be interposed against one who is not a holder in due course but also a holder in due course

DELIVERY  IS  NOT  CONCLUSIVELY  PRESUMED  WHERE  INSTRUMENT  IS INCOMPLETE

      Section 15 and 16 read together
 

BUT DELIVERY PRESUMED PRIMA FACIE

      But where an incomplete and undelivered instrument is in the hands of a  holder  in  due  course,  there  is  prima  facie  presumption  of  delivery which the maker may rebut by proof of non-delivery
      Where the custody of an incomplete instrument has been entrusted to another, who wrongfully completes and negotiates it to a holder in due course, delivery to an agent or custodian is a sufficient delivery to bind the drawer or maker.