No. There is no checking active at DO reference level
Yes. A unicity checking of the DO reference is carried out, irrespective of the status of the existing DOs for the depositor. The checking does not take the historical basis into account.
Yes, if not closed. A DO reference can appear several times, in the portfolio, provided that the previous references have the status 9-Shipped/Closed. The checking does not take the historical basis into account.