No.
$$\begin{array}{|c|c|c|} \hline \text {A} & \text {B} & \text {C} \\\hline\text {1} & \text {5} & \text {6} \\\hline\text {2} & \text {4} & \text {7}\\\hline \text {3} & \text {4} & \text {5}\\\hline \end{array}$$
Suppose this is the relational instance at any point of time.
Now we can see that $A\to BC$ holds for this instance, hence $A^+=\{A,B,C\}.$ (For every unique value of $A$, values of $B$ and $C$ are distinct.
But FDs are defined on the schema and not on any instance. So, based on the state of any instance we cannot say what holds for schema (there can be other instances too for $R$). At the best we can say that $A \to BC$ MAY hold for $R.$
PS: If we have a single instance where $A \to BC$ is not holding, it is enough to say $A \to BC$ does not hold for the relation $R.$