That is for the predictor to gear up his activity and keep a record of such trains. There are many trains which keeps getting extra coaches on a daily basis. Now if you expect everything to be handed over on a silver platter to the predictors, I am sorry to say the level of prediction is surely going to come down.
However historical the current rules may sound, I am sure while framing those people were logical and sensible enough to frame out the correct and apt ones. System isn't our enemy to preplan and get the tickets confirmed by lieu of extra coaches and/or auto-upgradation.
All...
more... these things take place at the last moment and are purely automatic. It is upto the predictors to take everything under consideration and then put up his prediction.