The passive capture of Wi-Fi traces using sniffers is a promising technique for characterizing the wireless activity of a target area without disturbing users with intrusive measurement tools. The main problem with this technique is that individual sniffers miss packets, which may lead to an inconsistent representation of the scenario. In this paper, we advocate that redundancy (i.e., collocating two or more individual sniffers) is necessary to achieve a reasonable picture of the wireless traffic at the time of the measurement. We formulate the notion of traffic completeness and investigate it experimentally by analyzing Wi-Fi traces obtained by up to 14 co-located sniffers (Raspberry Pi 4) in an office area. We make several observations, including the fact that all individual sniffers capture packets that none of the other sniffers capture. Our results confirm that, depending on the level of completeness that experimentation needs, redundancy is necessary. Moreover, we highlight the importance of characterization of the wireless environment. We define and analyze a few metrics for the characterization.