Norinco Type 54 vs Type 54-1 ?

[msmp5]

What's the difference between these two? I recently came across a pair of these pistols, both in 7.62x25, one marked "Type 54" and the other marked "Type 54-1". Both say "made in China by Norinco" on the left side of the slide; the 54-1 has import markings of "CSI ONT CA" on the right hand side of the slide, but the straight 54 has no import markings on the right side of the slide. Wondering if someone can explain this a bit? And what the difference is between these two models?