Just forgot to reply your one point.
"This would again create a confusion cz system would first try to allot to those eligible."
#
Well allocation in SS Quota (Lower berth Quota) is a guaranteed phenomenon at the time of booking if there are any berths of SS Quota left. At the time of charting, what PRS berth allocation logic does is, it tries...
more... to give preference to Senior citizens for lower berth, but there is no guarantee in this scenario(WL pax getting confirmed and getting lower berth).
##
Got hold of one of my mates working with CRIS, have asked him if he can help me out with complete requirement document for berth allocation logic or the design document. If I get that I will surely try to post the logic in simplified words.