Cullinane said, at some point, the panel missed the fact that milk has natural sugars in it.
Therefore, the naturally occurring sugars were missed from the label and the overall sugar content was incorrect.
"We wish it hadn't happened," Cullinane said.
It was expected labels would be reprinted and bottles put back on shelves in the next two weeks.
Cullinane baulked when thinking about what the overall cost of the mistake would be, but said cost wasn't driving any decision-making at this point.
"At this stage we just want to get it fixed."
Cullinane said the discovery and correction would not affect any of the company's other products.
The new product was created by different developers and a different process was used for figuring out nutritional information.
The drinks' nutritional information with the correction had more than double the sugar content printed on the original labels.
Latest test results showed the sugar per 100ml of the chocolate Breakfast Drink was 8.91g. Of that, around 6g was a naturally occurring sugar in the milk.
For the vanilla flavour, latest testing showed the total sugar per 100ml was 8.30g. Around 5.5g was lactose - naturally occurring sugar.
Each Breakfast Drink bottle is 250ml with the total sugar coming in at around 22g per bottle for the chocolate flavour and a little less than 21g for the vanilla variety.
The World Health Organization recommended our sugar intake shouldn't exceed 50g per day - though this did not include naturally occurring sugars such as that in milk.
Cullinane said he didn't yet know whether the drink would lose its five-star health rating.
Both flavours of Breakfast Drink were currently going through independent testing to "triple check" the sugar content.