@Dr.Dark is referring to the weapon cap for SVs. This is where an SV can only have 21 active weapons that can be fired by the player.
Turrets on all vessels do not have such cap, and will ALL fire at the target. No matter if you have 100, or just 1. They all work. Targeting works as follows:
Turret 1 acquires target.
Turret 2 attempts to fire at same target.
If turret 2 succeeds, it will fire. If it cannot target the “main ship” target it will attempt to find another target, or simply won’t fire at all.
Therefore, for maximum effect, make sure all turrets can aim at your intended target.
This is why people falsely claim that not all turrets will work, because turrets do not fire in sync with eachother. This creates the illusion of them not firing, but I can assure you from multiple tests and real live fire applications, this is not the case.