Thanks for helping me to make that conclusion. Based on the information that we have from other people that they sent their documents much earlier than you and they have not received their email yet, we can conclude that case number of time of visa availability has a significant effect on the date of receiving 2NL.
I am not certain that this relationship between the case number and notification email is correct. I will DEFINITELY be current in October (and the cut off numbers for Sept just came out and confirmed this) and I have not yet received an email.
My plan is to move ahead without it. This and past years' forums have stated that the email isn't too important for the process. It just makes us feel better that we have some official correspondence and direction.