DHCP

I am working at a branch office and have been tasked with changing out the DHCP scope to match the overall corporate IP address scheme. The main office assigned me an IP address range of 192.168.0.200 through 192.168.0.225. I changed the scope on Friday afternoon and came in on Monday morning to discover that only some of the workstations had picked up new leases from the DHCP scope. Any ideas as to what may be happening, what I might check or adjust?