I have purchased bolt and carrier assemblies from Stag and they have all had the gas key bolts staked. As far as the castle nut on Mass. compliant gun they only come with A2 stocks. Mass. Stag gun and lowers do not have pinned collapsible stocks, so I can’t know for sure what they do on stocks.
I do know that the parts I use from Stag have been the best quality.
I mostly assemble my own bolt and carrier assembly and I stake my own gas keys. I also lap the upper receiver so it is square to the barrel, I polish the bearing services on the bolt carrier and target crown the barrel.
I wasn’t aware that S&W assembled their own bolt and carriers I thought they purchased as a assembly. Are you sure about your information?