In my mind, it's not leftover, it 'belongs' to the next person in line (who can get there in time, obviously. But there must be plenty who could). Have I missed something really obvious?
Yes, you are. Logistics. By the time you’ve pissed about trying to contact all the “next in lines”, dithered about how they can get there and if they can, the vaccine is past it’s date.
This is why spares are being offered to specific groups like police, where one phone call will land the nearest 10 officers on the doorstep within 20 minutes.
There are experts planning all this. Mumsnet in all it’s wisdom does not have that level of expertise 