It's difficult to make any unified sense of what stated in OASIS and ECIC. The latter refers only to the Montreal Convention while OASIS refers in its main article to the Warsaw Convention and in its FAQs to the Montreal:-
"The airline lost / damaged my luggage, what can I do?
Should problems arise with your baggage, you should contact the airline immediately (before leaving the airport) and fill out a Property Irregularity Report; the reference number should be quoted on all further correspondence with the airline. You are covered under the Montreal Convention which states that the air carrier is liable for destruction, loss or damage to baggage for checked baggage.Under the Montreal Convention each air passenger can claim up to 1,000 "Special Drawing Rights" (approximately 1,200 Euro) for loss, destruction or delay of baggage. In the case of damage, the passenger has to make a written complaint within seven days from the date of the receipt of the luggage. In the case of lost luggage, checked baggage is considered lost if it has not arrived twenty-one days after the date on which it was due to arrive. If you cannot resolve the matter with the airline you may wish to consider taking the matter to the Small Claims Court."
Must be some way to clarify the situation?