LB quota is about 4 berths in each coach which is for ladies above 45 or gents above 60. If you opt "Book, only if at least 1 lower berth is allotted" for a lady 38 yrs , this LB quota berths wont be considered, But the other LB will be allotted subject to availability. Few of the LB will be designated as LB quota berths, not all.