I have a couple of NS Starfire Basses: one bought new in 2015 and one bought used/mint in 2016. Neither has either a printed or stamped serial # on the back of its headstock. I'm not up on when during NS production the ownership change took place, so can't say how that relates to these two basses. Both are festooned with Grover machines which appear to be factory equipment.
The serial # was printed on the back of the DeArmond SF Bass headstocks and (of course) stamped on the back of the headstocks of US-made Guild Starfire Basses.