Let analyze the issue.[ may be irrelevant to the question, if it, pls ignore]
lets break down the issue:
There are two requirement from the issuing bank concerned:
1. signed invoice= this is probably modification of sub article 18(a)(iv) with an objective to have all invoice signed.
2.3 copies= the total no. of invoice required by the isuing bank.This objective can be achieved in any combination abide by sub article 17(a).
Your wondering part:
its says that if the credit calls for a signed invoice in three copies, then one original and two copies will do.
with a logic:
a signature makes a document original
This wondering part is come into light due to sub article 18(a)(iv) that a commercial invoice need not to be signed. and probably making inperfect correlation between original document and signed invoice.
But i think this clause will be wonderring if it drafts on credit as follows rather than your posting:
3 copies of SIGNED ORIGINAL COMMERCIAL invoice must be presented.
Here copies and signed original is conflictied.
Now how reconcile the above point???