I really need to know now!

I also have the same screen, padlock with one diff. But what I have discovered Is that it has 3 stages of locking. Following a conversation with land rover, they say if the padlock is open and green then all diffs are open. Put it into rock crawl and you will see the padlock turn orange with 1 out of the 3 segments of the padlock illustrated. As more diffs begin to lock more segments turn orange.

I tested this. With wheels straight, low range and rock crawl selected I get 2 sections illuminated and an orange padlock. This means my cente and rear diff are locked. When I turn full lock right or left it unlocks the rear and keeps the centre locked, so I see 1 segment illuminated out of a possible 3.

I wonder if it was ever possible to have 3 locking diffs on a FF

Not from the factory.