Do all the Shards have holders?

[Quiver he/him]

So... random Shard related question. It's been taken for granted that when Adonalisum shattered, all sixteen shards were picked up by someone.

Do we have any WoB that this is the case? Is there any proof/speculation/whatever that might suggest that there may be a shard floating around without a vessel?

(I am terrible at realmantics, as this question should show)

[Pagerunner he/him]

Khriss identifies a group of sixteen people in Secret History.

Currently, Dominion and Devotion don't have Vessels, and they won't achieve sentience on their own, both because of how Odium had 'stuffed' them into the Cognitive Realm. (It's possible Ambition is in a similar situation, but Odium might not have figured that out when he had fought Ambition.) So, it's possible, with work, to leave behind a Shard without a Vessel. But it looks like they all started with one.

[Weltall]

Khriss and Nazh in Secret History confirm that there were sixteen at the Shattering who became Vessels and Brandon has talked about the sixteen as a group so we know that at least initially every Shard was held by someone. We also know that the Shards need a mind to control them and if they don't have one the magic will start to do screwy things and eventually gain sentience. It wouldn't surprise me if we see this happen at some point (perhaps not with an entire Shard but at least with a hefty chunk of its power) but right now the only Shards we know do not have Vessels are the four that Odium specifically splintered.

[Full Metal Rithmatist]

I believe they all had one originally but several have been killed and left their shards unheld.