You are correct.
The number of applications will increase if the charge pressure is reduced, however the applied pressure to the brakes will be less with each application and may not privide the required braking force.
Also if the pressure is reduced to zero you will have no emergency or parking brakes.
The accumulator is primarily there for parking and emergency use and if correctly charged wil give about 5 to 7 applications on most A/C that I have worked on.
When charging an accumulator it is important to ensure that all the fluid is released back to the tank, often by applying the brakes on and off during charging. This ensures that the correct volume if N2 as well as pressure is in the accumulator.
Hope this helps.