I'd ask in the beach forum as they are experts on ring labels in that forum. Far as the lower tone thing, I really don't think it's possible for the tone to be lower while the ID is the same. I think the audio/VDI are both based on a static conductivity reading of the target, so if it conducts high enough to be a 180 # then the tone pitch will also be outputting that way. But, not saying you didn't hear a distinctly different tone from it due to it's smoothness, warmness, softness, "roundness", etc. These BBS machines have the best audio details on the planet IMO and *most* gold sounds distinctly different from many forms of trash. Sure they overlap each other in audio qualities, but there is a generalization here and distinctness that separates many of them.
A gold ring can read as high as 180 due to the silver or copper or such they mix with it. Even the same K rings can have very different other metals mixed with the gold to change the conductivity I think. White gold for instance has I think nickle in it, which will make it read lower than you would suspect.
Again, great find...