In either case, things like accurate, that give you boost dice, are only used if it is on the primary weapon. If your secondary weapon is accurate, you will not get any boost dice when you roll.
When you make the initial roll, that is true. But if you do generate enough Advantage to activate the second weapon, then any inherent capabilities it brings to the table would then be available, whether that’s a boost die or an automatic additional Advantage, or whatever.
I believe that Sam made that pretty clear.