There is a chance that added sugars content prior to non-enzymatic browning and/or fermentation may be higher than the total sugars content of the finished food determined through chemical analysis. How do I approximate the added sugars value in this case?

The added sugars declaration should not exceed the total sugars declaration. In a case
where sugars added prior to or during processing are reduced through non-enzymatic
browning and/or fermentation, and the manufacturer chooses to declare the amount of
sugars added prior to non-enzymatic browning and/or fermentation, the added sugars
declaration could conceivably exceed the amount of total sugars determined through
chemical analysis. In such a case, you should declare the same amount for added sugars
as the amount of total sugars obtained through analytical testing for a serving of the food.