If the efficiency of CO2 consumption were 100%, then all CO2 consumed by the beverage filler and beverage carbonator would end up inside your package. This is never the case, as all the carbonation technologies and equipment are different.
Suppose you produce carbonated water with 9 grams (4,56 v/v %) of CO2 per 1 litre. You have 1 line with an output of 5 000 000 litres of carbonated water of all formats per month. If the line were 100% CO2 efficient, then you would put inside the bottles just 45 000 kgs or 45 tonnes of CO2 per month. That means that all the purchased CO2 reached the final product and there was zero waste of CO2.
However, the reality is different. If the beverage carbonator of the filling line is old or, say it is new but poorly designed, then the CO2 efficiency/CO2 Yield would be around 30-40%, which is normal. It means, that in order to put inside the bottle 9 grams of CO2, you spend 30 grams of CO2 (9 grams / 30% = 30 grams). Even the best and newest Krones Contiflow/KHS Paramix lines are able to demonstrate up to 75-80% CO2 efficiency if properly tuned, so 20-25% of CO2 is still wasted.
As a good approximation, the most straightforward way to calculate CO2 Yield of your carbonated beverage production facility is to divide the mass of CO2 consumed per month by the volume of carbonated drinks produced per the analyzed period.
For example, the beverage lines consumed 15 tonnes of CO2 per 1 month and produced 1 000 000 litres of carbonated water (remember to factor in different formats) with 9 grams of CO2 per 1 litre. So, you spent 9 tonnes of CO2 for the CO2 inside your product (1 000 000 litres*9 grams per 1 litre / 1000 grams / 1000 kgs) and wasted 6 tonnes of CO2. That means, that your CO2 yield is 60% (9 tonnes/15 tonnes).