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The are backwards compatible as far as I know. Dynamite Monkey is the guy to talk to. The mags have gone through 8 or 9 versions.
The mag on the left is the latest version (9th?) that came with my Gen 4 G17 It has the traditional cut out, the ambi cut out and the reversible cut out.
The mag on the right (what they call 4th gen?) has the traditional cut out, the ambi cut out but NO reversible cut out.