Let me explain you , how this thing happens
When ever you do availability enquiry , you will see like [some seats like 122 ]available or some rac like [rac 122/rac6 or rac6/rac 6 or GNWL 10/rac 100] or something like waiting GNWL 809/GNWL 564.
Waiting type could be other also in place of GNWL like RLGN.
What does all means.
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I am taking GNWL for example
out of two numbers GNWL 809/GNWL 564 -- the first one which is GNWL 809-- its booking status wait list. This will always keep on increasing.It means once all the berths were booked at least first time in availabilty and rac berths(whether cancellation happens or not, whatever may be the availabilty at that time, it could be waiting or rac or availability) then booking status becomes WL and first such waitlist become GNWL 1. Now at this time status could be GNWL 1/GNWL 1. it means current availability is ALSO GNWL 1. if someone who is confirmed ticket holder or in rac (if rac is also allocated in that train) cancels one berth in his/her ticket , the current status may become RAC if rac is alloted in that train. other wise if no RAC is there the ticket is confirmed.
So it may be like GNWL 1/confirmed- for that person. Next person who does the enquiry will get status as GNWL 2/GNWL 1.
Now say one more confirmed berth is cancelled by someone , the status becomes GNWL 2/CONFIRMED. bUT as of now this is shown on website as GNWL/available.
It clearly means that confirmed berth is available .
In most of the cases when some one books this type of availability the berth number is not provided at booking , but is allotted at charting time.
It could be possible that berth is allotted even before charting.