Andy Adcock
Worst person on Birdforum
You need the right light to see it but it can be quite obvious.My understanding is that they are named for the ring around the neck - more conspicuous in dead/taxonomy specimens which is what would have been looked at/handled when the species was named. Seen on eg wary birds but fair enough to say not a particularly enlightening name for the bird when experienced normally.
Ring-necked Duck stock photo
Stock photo Ring-necked Duck (Aythya collaris) adult male, swimming, captive. Buy a licence on mindenpictures.com
www.mindenpictures.com
Regarding the 'ring' on the bill, I presume it doesn't extend around the lower mandible but struggling to find shots that confirm this, so it, as previously pointed out, cannot be defined as a ring.