Absolutely and congrats for your sharp eye,

The units are not all tested together at the same time , but they are tested in batches. So there will be some differences related to the time of the day they were tested, and the units selected for a given batch. They are not tested in order.

The VOC doesn’t have a common baseline. You can read more about those sensors here: https://www.uradmonitor.com/smartcity-debate-iasi-2018/ . This is why we have the AQI VOC algorithm (similar to the Bosch BSEC library) that uses history data to compute a common baseline and provide comparable signals of identical amplitudes based on similar trend raw data. The auto test tool for this will only check that the value is in technically correct interval. The AQI VOC algorithm aligns the data between the various units or sensors (eg. BME680 vs MP503)

The CO2 sensor has an internal auto-calibration mechanism that triggers every 24hours and detects the lowest value to see if it gets close to the ambiental outdoor value of 400ppm. If this is the case, it will adjust an internal offset.

All in one these are the things you see between the various units in the report page.

Let me know if you need any additional details, and thanks for an excellent question.