When gathering from a site with DC as the expression for the filter, some DCs do not show up in the list when the site is enumerated.
Verify that the DCs that are not being populated by the Site enumeration are being properly resolved by your DNS server.
1. Open a command prompt
2. Type in the command ping <servername>, where <servername> is the name of the missing DC.
3. Using the IP Address retrieved from step 2, use the following command at the command prompt: ping -a <IPAddress>
4. Ensure that the name resolved in step 3 is actually the name of the DC that is missing.