Even though this thread is 3 years old, I had to reply on the topic of the black bobbin pickups, it seems these are correct and were a production anomaly for circa 1973 (though there were also basses produced with grey bobbin pickups with the usual 1973 date markings as well)
My 1974 Precision (neck date) also natural, with a white pickguard, has these black bobbin pickups, I was suprised when I looked at the underside of them because the bass sounded so good and they look very original from the top.
I did a bit more (a lot more) research and found a few sources that verified the above information, although there are just as many people asking the same question, and being told they have been added afterwards. I think some strat pickups of this era also had similar black bobbins.
Also when you look closely at the material you can see it has a hole punched through between the centre pole pieces, just the same detail as grey bottom pickups.
Anyway I believe my pickups are geniune.... so they are!