Love ya, Halliwax but gotta disagree with you here. The nipple in the V2 from my experience acts both as a d/s guide and well as a stop for the emitter, securing it to the the rest of the hilt. We don't know how much the V3/SS (while Shared Stunt I feel more correct and descriptive, V3 is better shorthand) was prepped to also house a motor, if at all, but considering how close it is to the raw cast in size and detail, I can only speculate that it wasn't as intensively worked on as the V2. I believe the V3 emitter lacks a collar and is only center-drilled for the it to slide over the driveshaft/tang and with a nipple similar to the V2 serving the same function. I think there's enough photo evidence to show that the fencing blades secured to the exposed center rod and only sat on top of the nipple.
To that end, I don't believe the nipple on the resin casts is a pour spout. In fact, I think they all came from the same mold. The Barge-Climb and the R2 cannon both sport the same clamp (the 3-holed upside down clamp) that still exists on the V3 currently, and pommel is in the same orientation to the clamp with a pommel cube just close to being centered with clamp box. I think evidence of this is the lack of bubbles in the casts, particularly around the emitter surface. Had it been poured from the top from the nipple, without having obvious risers/air vents to limit bubbles, it would have pockets around the pour area. It would also be a lot easier to cast it hollow from the bottom, whether by roto or slush-casting, or sticking a pipe through the pommel.
Something to consider is that there's little to suggest that the current grub screws in the windvane and the emitter the V3 sports currently were ever on the prop before Don Bies dressed it up for touring. There's not to say they weren't ever, but I find it a little convenient that many of the photos of it around the time are conveniently facing the grub screws away. The one photo of it being used in a walk-through with Luke and Vader on the catwalk, and its nipple is removed and held upside down, now that I don't know how that's done without it falling apart but I also don't know what was done to it at the time and why.