Something to consider is differences in absorption and context. One angle is coabsorbtion, where two molecules can be absorbed better together than apart. Another is binding, such as with lectins which can bind to some micro nutrients and prevent absorption. So if you add lots of something which is not bound like it naturally would be with foods that contain it then absorption may be disregulated and you may have wildly different levels absorbed than the nutritional label would suggest.

Adding lots of vitamin C to foods because of a cosmetic or preservative function may not be the best idea given how active it is in the body. Maybe it has a similar effect in the gut to what it does in the food in the packet, killing a bunch of microbes, and therefore could impact our gut microbiome. We don't have the data yet on the mechanisms, so we should withhold judgement for now.