The json file for Piglin Bartering contains an extra "set_count" function for items given out.
It's strange because it doesn't need to be there at all. It rerolls the count of items so that it will always be 1-5, regardless of what the actual set_count for the individual item is. Some items should even have a starting set count higher then the quantity of the extra set count given. Gravel, string, quartz, and shroomlights are all examples of this.