How much of an overdose? Double? Probably not much. Quadruple, but just once? Probably not much.
Way too much over a longer time? Well, many of the trace minerals can be toxic at overdose levels. For example, there is copper in Flourish Comprehensive. If you are repeatedly using too much the copper may build up to toxic levels, probably first noticed by a die-off of shrimp.
An active soil (finer than sand, with some organic matter) can lock up some of the minerals in trace nutrient mixes so that they are not free in the water. However, the soil has a limited capacity if you are adding a lot too much. Plants can usually remove the minerals they need from the soil, and plants can also take in more than they need of many nutrients.
A little bit- no big deal.
Somewhat more, but not over a long time- Plants may take it in, soil may remove it from the water column to keep a short term, not too large overdose under control.
More and over a longer time- Things will start dying of overdosing.
Cannot put any numbers on it. Each set up is different and has a different capacity to handle something like this.
What to do: Prune the plants. This will remove a lot of the excess that has ended up in the plants. You can rotate which plants to prune so the tank still has lots of plants to keep taking in these minerals. Be particularly careful to remove leaves as they start to die. Do not allow them to linger in the tank, releasing the minerals they were sequestering.