Our organisation have registered for DOI from Bowkers. We are in a process alloting DOI numbers to our Institutional publication and to the articles published by our scientist. My doubt is can we assign DOI numbers to the articles which has already given DOI numbers by the publishers. Example: A DOI number is alloted by cropscience journal to the article of our institutional authors.. shall I give our DOI number to that particular article alongwith the publishers assigned DOI ???