'67 Barracuda gas tank question: Why take only 8 gallons?

LOL Seems to be a similar problem in this thread here:

Trouble diagnosing problem

Check the vent has not clogged. Your vent is a simple tube going down the filler tube, through the floor gasket, and open ends inside the frame rail. Remove the tube and blow it out

Has the tank been damaged (and maybe then fixed) Pickup tube broke/ bent, not on bottom of tank?