Yes, i'm also going with the registration date as mentioned in the form and not marriage date. Because as per marriage certificate from India the marriage date and registration date are totally different.Marriage date question was asked many times in the forum and people who have done either of it have successfully got there OCI. So I am not sure what is the right answer for it. As it said registration date, I went for registration date which is different than the marriage date. In-person Ottawa submission.