That is correct. There is no such guarentee for WL'ed pax gettin confirmed. However, journey leg also matters a lot. If a confirmed pax having berth booked from A-C has canelled his ticket, then the system would try to allot the berth to the WL'ed pax having the same journey stretch from A-C. Even if a pax at WL1 has booked the ticket from A-B or A-D.
However this is a very minimal issue. I am having a long lasting debate with another well known person out here.If you could kindly reproduce...
more... the berth allotment/charting/booking logic out here, I would be really grateful to you.