Consistent quality can only be achieved by consistent and constant quality control.
Every single antenna we produce is carefully inspected and checked on VNA. Only the absolute flawless antennas are sent to the customer. Generally if antennas don't archieve VSWR below 1:1.3 then we dont send it to customer. We also pay big attention to quality of soldering connectors. We don't crimp inner pins in connectors - each pin is soldered to cable to archieve best performance in long peroid. 

Each order is individually processed and all antennas in same order are tuned to same frequency range - no matter how many you will order them.

With everything above said, our top priority is outputting highest quality parts, however, our antennas are produced by a human and mistakes can happen, despite our best effort for the contrary.