The problem that DHCPIP will be assigned after it is bound

After the DHCPIP is bound, it will be assigned a problem-Linux general technology-Linux technology and application information. The following is a detailed description. Prawns:
Is there a problem that other hosts will be allocated after a dhcp ip is bound to a MAC address?
The configuration is as follows:
Default-lease-time 600;
Max-lease-time 7200;
Log-facility local7;
Subnet 172.16.96.0 netmask 255.255.255.0 {
Option domain-search "van.com ";
Option domain-name "van.com ";
Option subnet-mask limit 255.0;
Option domain-name-servers 172.16.96.11;
Authoritative;
Allow client-updates;
Allow unknown-clients;
Ddns-updates on;
Range dynamic-bootp 172.16.96.120 172.16.96.122;
Option routers 172.16.96.5;
#172.16.96.0
Group {
Allow client-updates;
Deny unknown-clients;
Ddns-updates on;
Host {
Allow client-updates;
Deny unknown-clients;
Ddns-updates on;
Hardware ethernet 00: e0: 61: 02: 65: 05;
Fixed-address 172.16.96.120;
}
Host B {
Allow client-updates;
Deny unknown-clients;
Ddns-updates on;
Hardware ethernet d8: 5d: 4c: 1b: f0: ff;
Fixed-address 172.16.96.121;
}
}
}
Only three IP addresses are allocated to the above IP segments, which is 96.120 ~ 96.122.
If PC "a" and PC "B" have never been connected to DHCP, directly use a non-bound host PC "c" to obtain the IP address 172.16.96.120.
However, after PC "a" is launched, the IP address conflict is displayed. PC "c" gets the IP address of 172.16.96.121 in about one minute,
So why are bound IP addresses still allocated?
Is this the case or is there a problem with my configuration?
In addition, if a specific IP address is directly retained in the above configuration, the IP address will not be allocated?