It happens sometimes due to Quota Clearance, or in other words, when in some Quotas, The seats dont get filled, it goes to the lower Quota, lets say under GNWL 90% Seats fill and 10% seats remain, those 10% will be spread amongst lower quotas
And in Special Quotas, if the entire Quota doesnt book, the vacant berths will ALSO Transfer to Lower Quotas.
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So lets say you are in TQWL/15 and in Premium Tatkal there is atleast 20 Seats Available, your ticket WILL get Confirmed because the remaining WL will be filled with the 20 Available Berths of Premium Tatkal Quota.