Jeez. Just trying to actually help you.
The Wiki states that the gem itself can be claimed after visiting the Dream of Iaia for the first time. Now, while we can't always take the Wiki at its word (As it is inaccurate at times), I just wanted to check. In hindsight, I actually forgot that the person you hand the necklace to
is
within the dream, so I'm deeply sorry if I made you resort to pettiness.
To answer the question in the OP: no, there's nothing else required for the gem. Even if it's destroyed, you are able to reclaim it from the dude with the silly name. As you stated, you have completed one of the post-quest achievements and exhausted the dialogue, so there shouldn't be anything stopping you.
I can only assume that:
A). You have already claimed the gem and combined it with the ring, meaning that the physical ring you have is simply a duplicate. This seems unlikely, as I wouldn't expect a player of your calibre to forget something like that. I would agree with your idea that it should have its own achievement to help track it.
OR
B). There's a really specific bug related to your account, which isn't unheard of. If so, you have done the right thing in reporting it, but you are highly unlikely to receive a reply as that's not how they roll.
28-May-2022 04:49:14