If your sensor recalibratws to a baseline of 400 each day and you have a baseline of 700 that is a drift of 300 ppm per day or ca 100 000 ppm per year.
It's not going to drift by 300ppm per day - it'll pick the lowest value it saw and assume it was 400ppm. If that happens to be 700ppm every day, then it'll be wrong by 300ppm every day.
You see why this is a problem?