I have not yet seen a complete coin/holo set together in one place, but I'm pretty sure one exists... somewhere... I guess

I wouldn't be too sure. As far as I know there's only 5 people in the world currently holding 1000 BTC coins with intact holograms.
Well, there can be only one full set.
To be clear, only 1 500BTC bar exists. Only two were made, and one was redeemed.