No, not all Stageas have LSDs fitted. AFAIK, the ATTESA system uses electronically-controlled clutch packs in the centre diff, so there's always rear drive, and the split to the front is constantly variable. The diffs (both front and rear) are standard "single-spinner" units, but because there's generally so much traction available, the LSD is only really needed when you're REALLY pushing the car.
Have a look at the WikiPedia explanations of ATTESA, and how it's applied in Skylines, GT-Rs and other north-south engined Nissans.
There's also a few words confirming that the Stagea was the only RB25DET engined car equipped with AWD (scroll down to the R33 section).