I haven't bought Mosti's Barolo or Amarone kits but I have bought Cellar Craft's Showcase Amarone which they call Amarone STYLE. As others have noted, these two types use a specific varietal grape. But they also reflect very specific attributes regarding both special processing and the final resulting style of wine product.
Kit makers have had legal problems in this regard. Several years back, WE had big legal problems with their Chateau Neuf du Pape kits and were forced to re-title them Chateau du Roi or something like that. WE now describes them as similar in style to Chateau Neuf du Pape. You will note similar waffling from other makers as well.
Don't be surprised if Mosti is not forthcoming about what is in their kits. All the kit makers keep that as closely guarded proprietary information. And probably with good reason.
I think it is amazing that we accept as a given what the kit makers decide to call their juice. Truth is, they can call their kits about anything they wish and make them with a wide variety of other varietals (of any percentage) blended in, or God forbid, artificial colorings and flavorings. There are organic-based flavorings that I suspect are likely prohibited from use in American winemaking, but not in juice for winemaking kits. Remember, we are buying only juice, an agricultural product and not wine. For example, the U.S. wine labeling laws requiring at least 75% of a labeled varietal do not apply to wine kits!
So, if Mosti did agree their Barolo kits had nebbiolo juice it wouldn't mean much about what percent is in there or what else is in there!
There must be a compelling reason almost all the kit makers are based in Canada. I suspect the laws governing disclosure of contents of agricultural products like grape juice are much more lax in Canada than in the U.S. But I could be wrong.
NS