A crucial premise here is the non-persistence of accidents: in this classical theological account, one and the same individual accident does not remain unchanged across successive moments.
If power is an accident, identifying the power present earlier as numerically the same power later accompanying the act becomes controversial. Merely saying that 'the earlier power is still there' does not settle the dispute.
This is a premise of classical kalām, not an experimental law of modern physics. The debate over it directly affects the argument about when capacity and action coincide.