That question did come up for me a few days back when I started with VyOS and I came across “show dhcp server leases state all” does not report static-map leases in this forum.
tl;dr: VyOS before 1.5 use ISC DHCPD and it doesn’t have a way to know the in-use static mappings. It will work in 1.5 since the new DHCP server (KEA DHCP) handles is differently.
What I would have found helpful would be a way to see all the static mappings, no matter if in use or not. Something like show dhcp server leases state static. That seems to be possible and not too hard to implement.