Hello Vik,
As moomoo and I said earlier, due date doesn't mean much, however, in your case they specifically wrote about "due date being amended" in your gcms notes. So I'm thinking it may (or may not) mean something at the very least. Usually, as moomoo said, its a date by which someone should be looking at your life but doesn't happen always as it's automatically gets pushed back by the system.
However, you can find it under "assignment details" section on your gcms notes, found in the front (within first 4-5 pages) of your notes.
Hope it helps