Just CALL CZ (or email them) and tell them which model CZ you're using the Kadet Kit with.
The various models have slightly different slide stops, depending on the width of the frame and the caliber. The .40 frame's width is is different than the 9mm frame in the same full-size model, and the various 9mm models come in different frame widths. And, a .40 slide stop doesn't extend as far into the mag well as a 9mm slide stop... so it's less likely to catch the follower.
They should send you a new one, free.