Conditional Forwarders in 2008 R2

Hi

 I have 10 DCs in my child domain and in parent domain have 3 Dcs.

I don't have any DNS in root domain.

 I have all ADDNS in child domain and my parent domain DCs are pointing to child Domain ADDNS in TCP/IP properties on preferred DNS.

 As of now everything is working fine.

 But i can see some discrepancy in my child domain ADDNS settings as follows:

 1:- DC20, 21, 22, 23 & 24 has the same conditional forwarders updated to each other and except these 5 dcs, all other dcs don't have same conditional forwarders.

 2:- DC20, 21, 22, 23 &  24 has the ISP IP address details in the forwarders but other remaining DCs are having DC20, DC21 IP address in the forwarders.

 Also I have forest wide zone data replication enabled in the ADDNS.

I want to know that why its discrepancies in the same domain Active directory integrated DNS?