IMHO the idea that 18 shot SP01 mags are going to work correctly in the Pre-B guns is one of those urban legends that righteously needs to be debunked. Here's why.
The 18 round mags for the SP01 MAY work, depending on the individual pistol and the mags you happen to be sent - or it may not work at all. I forked over a painful $100 for a three pack of them a couple of years back for my 1991 CZ85. One inserted fine and functioned correctly except that it wouldn't hold the slide back on the last round, and still won't. The second one was an unacceptably tight wedge fit, and I do mean WEDGE FIT, and the third one ground to a dead stop a good 1/4 inch out. So I kept the first one to use with the '85, and rerouted the other two to my two CZ 85B's, which readily accepted them.
From this experience I'd have to say that using the SP01 18 shot mags isn't the cure it is often thought to be. Given my bad luck with this fix, especially when considering the obvious variations in dimensions from mag to mag, I think it's a crapshoot at best. And I definitely wouldn't pay the high price for a three pack of these mags unless I had another gun that could use them.
As cntrydawwwg pointed out, the factory 10 round mags work fine in my 1991 '85.
