The current Bandgap references are designed with such high-order precision say around 1ppm/oC which amount to say 1 mV variation over -40 to 120 oC. But I would like to know how much and it what way would such a small variation can result in the output/bit error of a DAC/ADC. Just bcoz the absolute value of Vref changes, does that mean, there will be overlap of the bit values. Can anybody help me?

Ok if I assume that in most cases , the absolute value doesnot matter much ( since it can be trimmed down .....I have some doubt here also) then , why does the variation in temperature of such high order say 1ppm/Celcius can affect the systems. Can anybody site an example or direct me to some materials regarding this.