A bag is only declared lost when the airline admits defeat and declares it as lost and then hopefully compensates you.

This is typically after 60 to 100 days. Until then it is missing bag. You must remember not all stations are as good as as they should be at updating WorldTracer with OHDs. And bags get pulled by customs, inadvertently picked up and taken by other pax, etc so it sometimes takes time to find them...

Quite often airlines will already know where your bag is if it did not make your flight. They can therefore open a file for you before you arrive at your destination and will be able to tell you where your bag is and on which flight it will arrive. In this case it is clearly a delayed bag!

I think people including airline staff often interchange the words lost, missing and delayed quite freely!