Here is a picture of the back surface of the old and new straps.
Thanks very much indeed Gary; my old and new straps both look like your new one.
So Zeiss sent me a new strap when I already had one; I feel guilty, but I had no way of telling, and I would have expected them to check my serial number, and say "you already have the new strap". I imagine it's not that simple…
Now, do I dare use the spare one for my nice 1984 Trinovid 10x40B? No, probably not