I seem to notice a correlation between single queuing and party queuing. For ex and high roulettes you have to have unlocked each and every instance before the roulette unlocks. That way, while queuing in a party, everyone has the same set of stuff unlocked, no way around it. Those roulettes where you have to queue alone, allow you to queue eveb if you haven't yet unlocked each and every instance the roulette contains. I'm fairly sure this is the only definition that separates the behaviour, why else would you have to unlock each hard dungeon to get the roulette. It's there just so that you can queue as party.