Subnet which are imported through Spreadsheet will have display name as Address and subnet mask if none is specified in display name column.
Subnet display name will not be overwritten if DHCP server and DHCP scope is added after import process.
Before import of subnets if you have DHCP scopes which in turn will create the corresponding subnets then Display name of imported subnet will not be over written by DHCP server scan.
So far we can generate two ways for generating subnet.One way is adding DHCP server and other possible way is adding subnet other than DHCP server scan(importing subnet through spread sheet,Automatic subnet discovery,Bulk add subnets).
First method you have chosen will be retained in IPAM.