For RailFans, the Journey itself is the Destination. - Sreerup Patranabis

Ques) What is "Chart Not Prepared" status?

Ans) The last booking chart for a train will be done at least 4 hrs prior to the schedule departure of the train at originating station.
But in reality, charts have been getting prepared 1 or 2 hrs prior to the actual departure of the train.
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situation of early morning or late evening trains, this might be prepared considerably earlier during the previous night itself.
A person's booking standing might change any time till chart is prepared.
Though quite uncommon, it is possible that an RAC ticket can change to wait-listed status.
It is also possible that booking relocated from WL to CNF can return to RAC or WL.
However none of this will certainly not happen for a ticket which was CNF while Booking itself.

Source: indianrailways.info