You have it correct. And in theory, yes a notch could be produced. But the minute you add back in the damping produced by the acoustic impedance of the terminus, add fiber or foam damping in the line, place the driver along the line instead of at the closed end, and account for the offset positions of the driver and terminus on the baffle the sharp peaks and deep nulls start to smooth out. The terminus output between the 1/4 wave resonances starts to be attenuated and the phase shifts a few degrees so the reinforcement and cancelling is not as dramatic. You start to get the rippled rolling frequency response typically associated with TLs.
Thinking about the measurement plots you linked, if they have designed a TL that when damped still has a deep notch at a frequency around 200 Hz, between the 1/4 wave resonant frequencies, when measured in a chamber with no boundary reflections then the design needs further work in my opinion. The damping does not appear to be very effective below a few hundred Hz. In a correctly damped TL, tall peaks and deep sharp notches should not occur. Usually you are left battling the ripple and use driver offset to tame it.
Thinking about the measurement plots you linked, if they have designed a TL that when damped still has a deep notch at a frequency around 200 Hz, between the 1/4 wave resonant frequencies, when measured in a chamber with no boundary reflections then the design needs further work in my opinion. The damping does not appear to be very effective below a few hundred Hz. In a correctly damped TL, tall peaks and deep sharp notches should not occur. Usually you are left battling the ripple and use driver offset to tame it.