Well, gud query!!!!!
As earlier example of mine about Godan Express, where PQWL was from LTT to ALD!!!
Now if that pool is having berth post its own PQWL clearance, the Pool will be shifted to clear on the GNWL, i.e. LTT-GKP or LTT-GKP(pool).
Its easier to allocate LTT-ALD quota to LTT-AMH OR LTT-GKP waiting, as the train is largely vacant in between LTT-GKP...
more... Quota.
Same logic goes everywhere for PQWL transfer into GNWL.
Now u say, two quota on same ticket, simply its utilization of one full quota against other quotar