The nearest thing to an applicable solution is to start a claim with Paypal for Item not as described (Which it undoubtably is) and specifying damage in transit, which is about as close as you can come to 'wrong item sent from Kentucy depot', although you should put this in as a footnote.

What will happen is that you will get a complet refund of all money paid and keep the item you got. The seller's funds will be put on hold for a week or so, then  released. They will not lose any money.

The Finnish buyer is the lucky one here, since they can do the same thing, get all their money back and keep the watch.

You could inform the seller that their money will be held and released and they should not get a defect for this. Clearly they have no knowledge of how the GSP works so will know nothing about error procedures.

The Paypal claim can be started without reference to the supposed delivery date.

You should not have any need to do anything else. If you do speak to an ebay CS person specify this is a GSP matter and ask to be referred to a specialist. The basic CS staff know nothing about the GSP and the only usful thing they can do is to refer you to a specialist.

There is nothing at all that the seller can do to help.

I have seen several accounts of this sort of mixup, in all cases they were settled as described above.