From Reddit: NO level sync when entering a dungeon with less that required players!

[Nekodar]

Well, even if you need one more person to enter, nothing says that person can't leave the dungeon once you're in, right? That's how we have the Solo Scholar Dungeon youtube videos =D

I'm aware that you can do it that way... I just wanted to know if anything was said about this applying even for solo entry, assuming the right options are selected of course.
From the most recent event I only recall it being an option for premade parties with less than otherwise required number of players. So, is solo a subset of premade party, or is it not considered at all...