Do you have a PCR slide stop to try?
If this is a Steel B-SA Frame, the PCR Stop will be too long
If you call CZ-USA they will ship you free correct slide stop. Now Kadet kits shipped with two slide stops. One is longer for (PCR).
The Kit should work correctly with the stock, B-SA Slide Stop
The two Stops that came with your new KADET Kit should be a PCR (the longer of the two) and one for a 75B ( did you try this one ? )
My 75B-SA Slide Stop is quite different than the one on a standard 75B .... not sure way
If you did not receive one with your Lower, then YES, CZ-USA will know which Stop is the correct Slide Stop for the B-SA Frame
My B-SA Slide Stop looks just like your "SP-01" Stop
And my old "B" Stop looked like the one you labeled "B-SA"
Looks like someone may have sent you the wrong Slide Stop
Just for Ss and Gs, try your SP-01 Slide Stop in your B-SA / KADET and see what happens