It might be that some manufacturer's give the weight of the complete part which would include bolts and others give the weight based on just the stem casting alone. But who really knows for certain.

You'll find that even the parts will vary in weight by what some of us consider significant at times. So don't expect what you see to be what you get in terms of weight.

I expect in most cases the weight to be the completely assembled part. That includes bolts.

I'm never sure though when viewing weights at online retailers, if that is the part weight from the manufacturer, or the weight they put in there for the box and everything.