This tip derives from observations of an exhaustive list of PNRs of this train and also from personal observations. Exceptions *might* occur in future, but so far I've hardly come across any such.
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In 3A, while booking if the status is GNWL AA/BB (for example in the status GNWL 45/78 AA=45, BB=78) , if the figure 'BB' is below 100, your ticket will, in 9 out of of 10 cases, come down to RAC at least, if not confirmed. So go ahead and book it!