I copied firmware from Deb8 to Deb9; however, the file name needed to change from BCM20702A1-0b05-17cf.hcd to BCM20702A0-0b05-17cf.hcd, so when I copied the file, it still didn't work. It took a while to see that the file mentioned in dmesg >>really<< wasn't present. Don't let it happen to you.