Where in About This Mac > System Report can you see whether I have the BCM94321MC vs. BCM94322MC?Anyway, Apple removed support for BCM94321MC from the Sierra driver…
If i remember correctly, BCM94321MC is one of the most common Broadcom Wi-Fi on 2008/early 2009 Macs, checked some of my old Macs around and I have the exactly same board on my MacBook5,2/early 2009 and on iMac8,1/early 2008. I think it's the same chipset on mini3,1 too, albeit with another form factor, have to confirm that later.
Latter Macs have BCM94322MC, this one has AirDrop.
If I have AirDrop working, then I must have BCM94322MC?