It is very nice of you to point out the policy of USCIS that primary and dependent should be approved together; I have been confused about this for a while.
I called USCIS and was lucky to talk to a nice lady; she said my hu*****and has been under "background investigation"--which has been done for everyone who files after 911. So my "background investigation" was cleared earlier than my hu*****and. She also said “Background investigation" usually takes 6-12 month. However, the lady does not know when the name was sent to "background investigation".
Anyone who has gone through "background investigation" please share your information. Thanks!