Are "unsaturated", "saturated" and "supersaturated" examples of variable composition?
Yes, they are.
A saturated solution contains the maximum amount of solute.
An unsaturated solution contains less than the maximum amount of solute.
A supersaturated solution contains more than the maximum amount of solid in a given volume of solvent.
Thus, in each solution the solute has a different concentration.
This demonstrates the variable composition of a solution.