I don't get in what context multiple interfaces/machines can have the same link-local address. Thanks in advance.
Two, or more, machines can have the same link-local address in every context, except the one where they are on the same link-local network. Routers strip off the frame from the packet, losing the link-local addresses, in order to route the packets, so the link-local addresses are confined to the link-local network.
For layer-3 link-local addressing, packet with link-local addresses are not allowed to be routed to a different network, so different networks can have the same link-local addressing.
The very name, link-local, really gives you the context where you cannot have the same addresses.