If you use dhcp static leases they are not visible in

show dhcp server leases state all

but if enabled dhcp monitoring you can see there

eg.

DHCP: Dynamic and static leases present for 192.168.10.136. DHCP: Remove host declaration LAN10_host2 or remove 192.168.10.136 DHCP: from the dynamic address pool for LAN10 DHCP: uid lease 192.168.10.51 for client 00:0c:29:xx:xx:2d is duplicate on LAN10 DHCP: DHCPREQUEST for 192.168.10.136 from 00:0c:29:xx:xx:2d via eth1 DHCP: DHCPACK on 192.168.10.136 to 00:0c:29:xx:xx:2d via eth1

reserved lease could be good solution for this also

On ISC DHCP manual this is explained
https://kb.isc.org/docs/isc-dhcp-44-manual-pages-dhcpdconf#reserved-leases

If I understood correctly, reserved lease support could help to have more transparency and the logic of working would be more straight forward. Would be good feature to have and I know at leaste one more person than me that would benefit on this. :)

this is my first feature to suggest, so might contain weirdness.