Some of the points that I read from various websites w.r.t CP ( There is no Government document available)
After NVC fees is paid, a parcel (documents) will be sent to the applicant. The applicant can delay the consular interview for one year from the day of receipt of the parcel , provided he submits valid reason for the delay.
On the day of the interview the applicant is given a clear verdict, pass or fail.
If fail, he is eligible for re-interview without new application, fees etc within one year.
If pass, he is stamped with immigrant visa which is valid for only 6 months, within that he must enter the US to get his physical GC. Otherwise the immigrant visa is not valid meaning the visa number is wasted.
I am really confused with the time limit ( 1 year interview time 1 year appeal time), though we all know NVC sends fee notices well ahead. As S said, we will ever know how they operate.