Generally GNWL do not convert to CNF if it remains waitlisted a few days before the date of journey. It also depends on RAC capacity.
In your case, 12392 has 140 aound seats in RAC which makes it even more difficult to become CNF.
So first of all you have to get 24 cancellations to be in RAC, then 140 further cancellations to get cnf status before charting.